Organotin

Antifouling paints incorporating tributyltin (TBT) compounds were introduced in Europe in the 1960s and within a decade were in widespread use. The French shellfish industry experienced problems with the cultivation of oysters in the 1970s, and scientific investigations suggested these were caused by TBT. Many of the problems were resolved when the use of TBT paints on small boats was banned in 1982. Similar effects were noted in the United Kingdom, and controls were first introduced to limit the TBT content of paints. These controls proved insufficient to protect shell fisheries and the general environment, and new problem areas were seen in fresh waters and where TBT was used on nets in salmon farms. The United Kingdom therefore banned the use of TBT, except on vessels >25 m, in 1987. A number of European countries have taken some action, or are considering doing so, and a European Community Directive will harmonize the regulations of member states by 1991. Scientists and policy makers are still undecided on whether TBT antifoulants used on large vessels constitute a risk to the environment during normal operations; current research is addressing this issue. Unregulated drydock practices involving cleaning and repainting can, however, lead to discharges containing unacceptably high concentrations of TBT; steps are therefore being taken to control these discharges. The need for further action is being considered within the international conventions (Paris, Helsinki, and Barcelona) and in the International Maritime Organization.

An historical overview of the use of organotin compounds as biocides in antifouling boat-bottom paints as well as a wide range of national and international regulatory and legislative options for policy and decision makers is presented and discussed in this chapter. The discussion includes the US Antifouling Paint Control Act of 1988 as well as international regulatory policies and practices from the United Kingdom, France, Switzerland, Germany, Japan, the Commission of the European Communities, and international conventions. The impact of present regulatory policies and practices are reviewed in accordance with economic and environmental costs and benefits, such as the effectiveness of regulations by developed countries at reducing local environmental concentrations as well as the shift of organotin-related environmental hazards (and associated economic loss of shipyard business in developed countries) to lesser developed countries (due to inexpensive labor and less stringent environmental regulations), which could be referred to as the transfer of contamination to those countries least able to deal with it. The following regulatory options are recommended as the most promising: (1) limit the release rate of organotin compound(s) used in copolymer antifouling paints to the adjacent water column and national water quality standards; (2) restrict the use of organotin compounds on mariculture structures, piers, and utility cooling water intake and discharge pipes; (3) develop a special antifouling coating R&D user’s port and harbor dockage fee(s); and (4) institute a vessel certification system by the International Maritime Organization for vessels using toxic antifouling coatings to provide a source of funding for the development of national research and development (R&D) programs for the most cost-effective handling, collection, storage, treatment, processing, and disposal of hazardous and toxic antifouling paint wastes from ships, dry-docks, and contaminated bottom sediments.

This chapter describes direct determination of sub-nanogram amounts of methyl- and butyltin compounds, particularly tributyltin, in aqueous environmental samples, plant extracts, and shellfish extracts by two similar methods. Both procedures use purge-and-trap methods following derivatization with sodium borohydride that allows concentration of organotin hydrides in a trap at liquid nitrogen temperature (-196°C). The organotin hydride species are eluted from the trap and are atomized in a quartz burner mounted in an atomic absorption spectrophotometer. The chapter discusses advantages and disadvantages of the two methods. Automation of one method permits near-real-time, aboard-ship determinations of tributyltin in seawater under in-situ conditions.

The marine antifouling agent tributyltin and its degradation products were determined in estuarine water by in-situ hydride derivatization using aqueous sodium borohydride with simultaneous extraction into dichloromethane. The butyltin hydrides were determined using gas chromatography with tin-selective flame photometric detection. The detection limit for tributyltin in a 200-ml water sample is 5 ng l^-1 (0.017 nM) by using this method. An aqueous tributyltin solution prepared by the National Institute of Technology and Standards (formerly the National Bureau of Standards) for a 35-laboratory comparison was analyzed by the new method. The result obtained by the new method is within 4% of the mean value of the determination for the 35 laboratories and within 9% of the value determined by neutron activation analysis. Fourteen marine and estuarine water samples were analyzed for di- and tributyltin in an interlaboratory exercise. For tributyltin, agreement between the new method and an existing one was within 20% for 9 of the 14 samples.

When analyzing environmental samples for tributyltin (TBT) and its breakdown products, it is important to speciate the various organotins that may be present in the samples. Most commonly used methods require a derivatization step to form volatile organotin hydrides or tetraalkyltin derivatives. The tetraalkyltins formed by reaction with Grignard reagents are stable compounds that are readily separated by gas chromatography and produce characteristic mass spectra that are easily interpreted. Various types of Grignard reagents and solvents have been used in the published methods for the analysis of TBT in environmental samples. When the longer chain (pentyl and hexyl) derivatives are formed, sample extracts can be concentrated to small volumes without significant losses from volatilization.

Gas chromatography with modified flame photometric detection has been shown to be a sensitive and somewhat selective technique for quantifying butyltins. However, the complexity of environmental extracts means that the only way to identify butyltins positively is with mass spectrometry. Gas chromatography-mass spectrometry, in combination with either electron ionization or positive chemical ionization, has been the most commonly used method. Qualitative identification of butyltins has usually been accomplished by full scanning and is facilitated by the characteristic isotopic pattern displayed by tin (10 stable isotopes). Selected ion monitoring has been the technique used most often for quantification by mass spectrometry. Mass spectrometry-mass spectrometry, alternative ionization methods, and stable isotope monitoring are all techniques that have also been applied to the analysis of butyltins by mass spectrometry.

Analytical methodologies have been developed over the last decade to quantify tributyltin in sediments and tissues. The methods involve extracting the substance from solid matrices with either an organic solvent (sometimes acidified) or an acid. Tributyltin (TBT) is then converted to a more volatile compound, either an alkyl or hydride derivative to facilitate separation from potentially interfering compounds and subsequent detection by gas chromatography, atomic absorption spectrophotometry, or mass spectrometry. Detection levels reported vary by more than an order of magnitude, but accurate quantitation at concentrations <10 ng g^-1 appears possible. Experiments conducted with oysters (Crassostrea virginica), exposed to TBT in the environment indicate that natural variability in TBT concentrations is such that ten replicates, were required to assess contamination at a station within a 95% degree of confidence.

This chapter reviews, evaluates, and critically compares the major techniques for the determination of butyltin species; discusses an analytical protocol for good laboratory practice; and presents results of several interlaboratory comparisons, including the certification of PACS-1 (the world’s first certified reference material for butyltins). The certified concentrations for tributyl-, dibutyl-, and monobutyltin are 1.21 ± 0.24, 1.14 ± 0.20, and 0.28 ± 0.17 mg Sn kg^-1 of dry sediment, respectively. The uncertainties are 95% confidence intervals for the analysis of an individual subsample.

The objective of this chapter was to collect, synthesize, and interpret data on acute tributyltin (TBT) toxicity for both freshwater and saltwater organisms. Survival of test organisms (LC₅₀) was the most frequently used endpoint for these experiments, although other sublethal parameters were also evaluated. Tributyltin toxicity data were evaluated for 29 freshwater species and 56 saltwater species. Most of the freshwater data and approximately half of the saltwater data were generated from experiments using nominal concentrations of TBT. Acute toxicity data generated from studies using nominal concentrations are suspect because TBT is hydrophobic and tends to adsorb to most contact material. Tributyltin also degrades in solution over time. The most sensitive freshwater species tested was the coelenterate Hydra sp. [96-h LC₅₀ = 0.5 µg l^-1 tributyltin oxide (TBTO)]. The bluegill (Lepomis macrochirus) was the most resistant freshwater species with a 96-h LC₅₀ of 240 µg l^-1 TBTO. Copepods and mysids were the most sensitive saltwater organisms with acute effects reported at TBT concentrations of 0.4–0.5 µg l^-1. Adult oysters were reported to be the most resistant saltwater species with 96-h LC₅₀ values >200 µg l^-1 TBT.

This chapter examines chronic toxicity of TBT through a discussion of five comprehensive studies performed during the last 8 y. The studies share the following characteristics. They are experimental studies conducted under laboratory conditions and designed to demonstrate a causal relationship between TBT exposure and a sublethal response, which was usually reduction in growth or abnormal development; Biol.ogical endpoints, such as metamorphosis or hatching, usually defined the period of observation; and experiments lasted more than 96 h in all cases. The studies are characterized as a progression of exposure levels that began above 1 µg l^-1, but dropped to 1–10 ng l^-1, concomitant with increasingly sensitive chemical analysis methods for TBT. The lowest levels tested are similar to those found in many nearshore and estuarine habitats. Test organisms include developmental stages of fish (Leuresthes tenuis), decapod crustaceans (Rhithropanopeus harrisii), mysid shrimp (Acanthomysis sculpta), oysters (Crassostrea gigas), and clams (Mercenaria mercenaria). Results of these studies demonstrate a range of taxonomically correlated sensitivity to TBT of two to three orders of magnitude. Fish and crab larvae were most tolerant, with exposures in excess of 1 µg l^-1 causing notable reductions in growth or survival. Mysids formed an intermediate group, with a sensitivity about one order of magnitude less. Clams and oysters are the most sensitive group, showing significant sublethal effects in TBT concentrations of 10–50 ng l^-1. The taxonomic pattern of sensitivity depends, at least partially, on possession of metabolic pathways to rid tissue of TBT. Studies with molluscs clearly show a ca usal relationship between TBT exposure and adverse sublethal effects that is consistent with observations made in field studies.

Data from laboratory and field studies on the effects of tributyltin (TBT) on the oyster Crassostrea gigas are presented in order to provide a framework for the use of the species as a bioindicator when monitoring for environmental concentrations of TBT, and for monitoring for harmful effects of TBT on marine ecosystems. Concentrations of TBT in tissues have been demonstrated to reflect concentrations of TBT in the water column. Shell thickness index and accompanying loss of meat yield in the oysters have been shown to be related to tissue concentrations of TBT or concentrations of TBT in the water column in a readily predictable way. In field transplanting experiments, tissue concentrations of TBT >0.2–0.3 µg g^-1 occurred concomitantly with a decrease in shell thickness index in the oysters, demonstrating that harm was occurring to a valuable marine resource. Deployment of C. gigas in the field has been shown to be a useful component in programs designed to monitor long-term changes in TBT concentrations. It is proposed that the presence of normally shaped C. gigas oysters yielding good meats are indicative of concentrations of TBT of <10 ng l^-1

The Bassin d’Arcachon, on the southwest Atlantic coast of France, is an important oyster-rearing area. From 1976 to 1981, the oyster industry was disturbed by shell abnormalities and by a drastic reduction of reproduction. As a consequence, the number of oyster farmers declined by 50%. The phenomena were consequent to a large increase in pleasure-craft activities in the bay; tributyltin compounds released from antifouling paints were suspected as the main cause of these abnormalities. The failure of larvae to survive the D larval stage was assessed experimentally by using the Crassostrea gigas embryolarval bioassay. At first, it was established experimentally that the use of tributyltin compounds was dangerous in oyster-farming areas. Above 1 µg l^-1 tributyltin (TBT) acetate, fertilized eggs cannot develop to the D larval stage; at 1 (µg l^-1 the D larval stage is reached, but all larvae are abnormal and die within a few days; from 0.5 to 0.05 µg l^-1 abnormalities and mortalities are still considerable (>78% over a 12-d period), and larval growth is strongly affected. At 0.02 µg practically no action is observed, and this value seems to represent the threshold tolerance level of the larvae. On the other hand, neither low nor varying temperature could explain the lack of larval growth observed in the field; the failure in larval development could not be attributed to the action of TBT on the gamete viability from Arcachon adult oysters, or to its direct action on embryos and larvae. In 1981, D larvae isolated from the plankton of the Bassin d’Arcachon were reared in the laboratory, in seawater collected at the same place and time as the larvae. In the field, the stomach of the larvae remained uncolored (absence of food), and the larvae did not reach the early umbo stage; in the laboratory, larvae of the same brood stock fed normally (stomach well colored), and reached the early umbo and the umbo stage 12 d after the beginning of the experiments. From this it was supposed that D larvae in the field could not find the appropriate food required during the first days of their pelagic life; this was probably due to a disturbance in the development of the nanoplankton caused by the action of antifouling paints containing organotin compounds. Since the ban on TBT-based antifouling paints was put into effect in 1982, the Japanese oyster has reproduced on a commercial scale every year in the Bassin d’Arcachon.

Most stenoglossan gastropods are gonochoristic (i.e. the sexes are separate). During the last two decades, the phenomenon of ‘imposex,’ the development of male sex organs on the female, has become increasingly prevalent, to the extent that >40 species worldwide are now known to exhibit the syndrome. Initial evidence linking imposex to the presence of the leachates of marine antifouling paints containing tributyltin (TBT) as a biocide was provided by studies of the American mudsnail Ilyanassa obsoleta, but no deleterious effect on its reproductive biology was detected. However, recent investigations of imposex in the European dogwhelk (Nucella lapillus) have demonstrated that in this species the effects of TBT can be profound, since breeding can be inhibited causing populations to decline and eventually disappear. This chapter summarizes the evidence that TBT pollution is responsible for the disappearance of N. lapillus in areas close to centers of boating activity.

Two methods of measuring the intensity of imposex in N. lapillus are described, namely the relative penis size (RPS) index and the vas deferens sequence (VDS) index: these indices provide indications of the relative development of the female penis and of the associated vas deferens. When fully developed, vas deferens tissue blocks the oviduct preventing the release of egg capsules, thus rendering the female sterile. Field surveys of much of the UK coastline demonstrate that the intensity of imposex, as measured by both indices, increases markedly with proximity to sources of TBT such as harbors and marinas. Close to sources, females are sterile, breeding activity has ceased, and populations are declining or have disappeared. Transplantations of animals from ‘clean’ sites to such contaminated areas promote imposex in the transplanted animals. Laboratory experiments in which animals were reared from the hatchling stage to maturity at 2 y of age show that at an ambient TBT concentration in water of 1–2 ng l^-1 Sn imposex is fully developed; at ⩾3 ng l^-1 Sn all females are sterilized. At higher concentrations (⩾10 ng l^-1 Sn) oogenesis is suppressed and is supplanted by spermatogenesis. Laboratory and field data indicate that imposex in N. lapillus is initiated at an ambient water TBT concentration of <1 ng l^-1 Sn. The high sensitivity of this response provides one explanation for the fact that imposex is found throughout the species’ geographic range except in remote areas (e.g. parts of northwest Scotland). In those areas where TBT pollution exceeds 2 ng l^-1 Sn, the sterilizing effect of imposex is apparent in the lack of breeding activity and dwindling population numbers.

The effects of tributyltin (TBT) exposures ranging from 1.4 to 2500 ng l^-1 were examined on a broad spectrum of shallow-water organisms in long-term flowthrough bioassay tests performed at Hawaii and San Diego sites. Tributyltin was obtained as leachate from panels coated with various antifouling paints. Mature fouling communities at Hawaii sustained major reductions in species and individual abundances at TBT exposures ⩾500 ng l^-1. Taxa most severely affected were those of low phyletic level and species with a high surface area of soft integument. TBT concentrations ⩾100 ng l^-1 caused significant reductions in settling epifauna of low phyletic level. Hawaiian infauna experienced abundance reductions of ~ 50% at 500 ng l^-1 TBT. Affected groups included nematodes, polychaetes, tanaids, isopods, bivalves, ophiuroids, and sipunculids. Abundances and mortality of benthic algae, macrocrustaceans, and fish were unaffected by TBT concentrations up to 2500 ng l^-1. Bioconcentration of TBT was found to be very low in swimming crabs and moderate in anchovy fish. Adult American oysters of the Hawaii experiments were unaffected by TBT exposures up to 1800 ng l^-1 and showed TBT bioconcentration factor (BCF) values that were inversely dose dependent, ranging from 19 600 to 35 000 at TBT exposure levels of 82 and 2 ng l^-1, respectively. Reduced growth occurred in San Diego juvenile bay mussels at 70 ng l^-1 TBT; and their BCF values were inversely dose dependent, ranging from 23 000 to 66 000 for TBT treatments of 450 to 6 ng l^-1, respectively. In spite of possible captivityinduced stress during San Diego tests, juvenile American, European, Olympic, and Pacific oysters showed no growth effects from TBT exposures ⩽200 ng l^-1. Growth rates and survival of adult Pacific oysters during Hawaii tests were slightly reduced by TBT concentrations of 13 and 29 ng l^-1. However, those oysters may also have been nutritionally stressed as indicated by growth, survival, and condition indices of tank oyster controls, which were substantially lower than those of field controls. Pacific oyster BCF values were inversely dose dependent and ranged from 31 600 to 88 000 for TBT exposures of 29 to 14 ng l^-1, respectively.

During nine field-transplant experiments (1987–1990), juvenile mussels were exposed to mean tributyltin (TBT) concentrations from 2 to 530 ng l^-1 for 12 weeks under natural conditions in San Diego Bay. Mussels were used as biological indicators and monitored for survival, bioaccumulation, and growth. Mussel growth was the primary biological response used to quantify TBT effects. Chemical analyses were used to estimate TBT contamination in water and mussel tissues. Integrating intensive measurements of chemical fate and biological effects increased the environmental significance of the data. Multiple growth measurements on individuals increased the statistical power. Size effects were minimized by restricting test animals to 10–12 mm in length, and methods were developed to minimize handling efffects. This monitoring approach also permitted documenting temporal and spatial variability in TBT and its effects that have not been previously reported. Survival, bioaccumulation, and growth were generally higher than predicted from laboratory studies. Survival was not directly affected by seawater or tissue TBT concentrations. Growth was significantly related to both seawater and tissue TBT, with the bioconcentration factor inversely proportional to seawater TBT concentration. Threshold concentrations always causing significant reductions in juvenile mussel growth are estimated at 100 ng l^-1 TBT for seawater and 1.5 µg g^-1 TBT for tissue, but growth could be affected by much lower concentrations of TBT under the most adverse conditions. Temperatures above 20°C were also found to reduce juvenile mussel growth rates.

Tributyltin (TBT) is accumulated by all taxa that have been examined. Typical tissue burdens range from undetectable levels to as high as 7 µg g^-1 (wet weight). Molluscs, as a group, exhibit the highest tissue burdens and also the highest bioaccumulation factors (BAF). Some microorganisms are also notable accumulators, but in this case adsorption to the biofilm (predominantly polysaccharides) rather than sequestration within cells is an important mechanism of uptake. Crustaceans and fish generally accumulate lower burdens of TBT, probably because they possess enzymatic capability to degrade and excrete TBT. Bioaccumulation factors (BAF) as high as 50 000 have been reported, but the route of uptake (e.g. from water or food) was not necessarily differentiated during the experiment. Experimental studies have specifically examined uptake from water, where calculation of a bioconcentration factor (BCF) is appropriate. BCF values range up to 10 000. Both BAF and BCF values are higher than would be caused by partitioning processes alone. Binding is thus proposed as a mechanism that explains enhanced accumulation. A scheme to explain bioaccumulation is presented that proposes a role for (a) chemical speciation of butyltin with major anions in natural waters, (b) routes of exposure, (c) role for partitioning and binding to control both the kinetics of uptake and burdens in tissues, and (d) contribution of depuration mechanisms to control tissue burdens. Findings presented in this review support the use of biomonitors for TBT contamination, but the tissue burdens of TBT in biomonitors likely reflect a steady-state distribution of TBT in all compartments of the ecosystem rather than concentration in a single compartment (e.g. water). While the topical issue of tributyltin use diminished due to restrictions on its use, this compound provides several important opportunities as a model compound to increase understanding of bioaccumulation processes and environmental compartmentalization, in general. Some further studies may thus be warranted.

The bioconcentration of tributyltin (TBT) by oysters was examined in laboratory and field experiments. The bioconcentration factor (BCF) in laboratory experiments ranged from 5940 to 15 460 for uptake from solution (TBT concentration: 283 ng l^-1 in experiment 1; 415 ng l^-1 in experiment 2), while the BCF for uptake from suspended sediment (TBT concentration in water + sediment: 259 ng l^-1) was 9179. The BCF for the field experiment was 21 971, which is of a similar order of magnitude to values derived from laboratory experiments. Time to 90% of equilibrium was estimated to be 42–49 d in the laboratory compared with an estimated 56 d to equilibrium in the field.

Reliable measurement of the rate of release of tributyltin (TBT) from antifouling paints is important for a number of reasons, principally for minimizing the potential environmental impact on nontarget organisms. When the TBT is chemically bound to a key constituent of the paint, its release rate is controlled by the rate of hydrolytic cleavage of the chemical bond; therefore, the release rate becomes an intrinsic property of the paint. When the TBT is present as a mixed component of the paint, its rate of release is not controlled and often is much higher than necessary for antifouling performance.

Laboratory measurements of the TBT release rate have shown that it can be measured reliably. These measurements provided the following information: (1) release rates of different paints range over several orders of magnitude; (2) freshly painted surfaces show an initial rate of release very much higher than the subsequent ‘steady-state’ rate; (3) temperature dependence of release rates demonstrated that the release mechanism involves a chemical reaction (hydrolysis) in those formulations where the TBT is chemically bound; (4) reduction in release rate when the pH is lowered also indicates that the primary mechanism is hydrolytic cleavage of the carboxyl-TBT bond, which releases the biocide allowing it to diffuse out; and (5) for the chemically bound TBT paint formulations, reducing their TBT content reduces the release rate as well as the surface softening and resulting hull smoothing. The rotating cylinder method for measuring the release rate in the laboratory has been applied by the US Environmental Protection Agency (US EPA) to regulate the use of TBT paints. This action achieved the following results: (1) paint suppliers became aware that the biocide release rate is an intrinsic property of the coating and has a direct bearing on evaluating potential environmental consequences from that product; (2) many TBT paints were found to have release rates unnecessarily high for antifouling protection and therefore placed an unnecessary burden on the environment; and (3) the US Congress, in enacting regulatory legislation, and the US EPA, in implementing such legislation, incorporated limits of TBT release rates as one key element in the regulatory action, removing thereby a large number of unacceptable products from the market and making a total ban unnecessary. Nevertheless, the rotating cylinder method appears to be flawed in that it simulates more closely the condition of a ship under way than a ship at rest in a harbor; consequently, very much higher biocide release rates are measured by this method than is actually the case. The rotating cylinder method, as it is currently used, can be improved by increasing the number of measurements and eliminating the current practice of regressing a single data point through the origin of the time-concentration plot to determine the rate of release.

Release of TBT in the environment is complicated by the presence of a biological film on the painted surfaces. This biofilm or slime layer consists of a complex community of microorganisms that presents an attractive environment for large settling organisms such as barnacles or tubeworms. The microorganisms in the biofilm become acclimated to the TBT biocide. As TBT is released from the paint surface, it concentrates in the biofilm due to exudates from the microorganisms, creating a hostile chemical environment that prevents permanent attachment of fouling organisms.

A novel, simple apparatus, easy to use in the laboratory or the field, has been developed to determine the minimum effective biocide release rate needed to prevent the attachment of settling organisms. The apparatus simulates different rates of release of biocides, and can be positioned in the marine environment and exposed to settling organisms. Data collected in this way will establish the optimum rate of release for a given biocide; that is, the minimum rate needed to prevent attachment by fouling organisms and at the same time to make a negligible impact on the environment. This information can then be used by paint chemists to formulate an antifouling paint with a high level of confidence that the new paint will perform well and meet regulatory requirements.

Environmental loading factors for tributyltin (TBT) were studied in Pearl Harbor, Hawaii, between 1987 and 1988. During this period three test ships were painted with TBT-containing antifouling paint. The drydocks used to paint the vessels were monitored for overspray and discharges to both the harbor and the sewer system. Use of extensive dry-dock cleanup procedures, including masking 50% of the drydock floor, resulted in discharges to the harbor of <15 g TBT. Harbor concentrations were largely unaffected by TBT discharges of <3–149 ng 1^-1 from the drydocks. Cleanup procedures were found to be successful in removing at least 99.8% of the residual paint overspray from the dry-docks, thus eliminating environmentally significant discharges to the receiving waters.

The TBT flux from underwater hull coatings was evaluated by a device for measuring in-situ release rates, which documented order-of-magnitude differences (0.1–2.8 μg cm^-2 d^-1) in release rates among types of coatings. Tributyltin loading from the test ship hulls, ranging from 2 to 115 g d^-1, generally covaried in a linear fashion with regional mean concentrations of TBT in the water column. An empirically derived model was used to predict future water column concentrations of TBT in Pearl Harbor of <10 ng 1^-1 from Navy use, assuming application of low-release-rate (<2.0 (μg cm^-2 d^-1) paints and effective drydock cleanup procedures.

Studies into the fate and persistence of tributyltin (TBT) in marine, estuarine, and fresh water environments have been conducted in diverse geographic regions and under various experimental conditions to determine rates of degradation and loss. Microbial degradation in water was found to be the most important process limiting the persistence of TBT in aquatic environments. Photolysis and chemical degradation were not significant in the degradation of TBT. Degradation studies were conducted using unfiltered seawater and fresh water incubated under natural conditions with sterilized controls from several geographic regions in the United States and Canada. Degradation half-lives were found to be in the range of 4–19 d in seawater and from a few weeks to several months in Canadian fresh water. The principal degradation product of TBT was dibutyltin (DBT) with lesser amounts of monobutyltin (MBT) formed.

The behavior of TBT and its degradation products was evaluated by introducing radiolabeled TBT into a mesocosm (13-m³ enclosure) to simulate a marine ecosystem including benthic sediments. Tributyltin disappeared from the water in the mesocosm initially at 0.20 d^-1 (20%) and slowed to ~0.10 d^-1 after 15 d. Degradation accounted for the greatest loss of TBT, with transport to the sediment and possibly the atmosphere (volatilization) accounting for the other losses. Degradation proceeded through the process of debutylation to DBT and to MBT with substantial formation of MBT directly.

Degradation of TBT in sediments appears to be associated with two independent processes: (1) a rapid abiotic chemical degradation of dissolved TBT has been identified in fine-grained sediment-water mixtures with a short half-life of 2–4 d; and (2) biological degradation as measured in marine and freshwater sediment, which is much longer, with a half-life of several months.

Environmental butyltin measurements provide additional evidence of the rapid degradation of TBT. Concentrations of MBT and DBT in the water column tend to co-vary with TBT levels, and higher percentages of butyltin degradation products (85–90%) were found in regions with long water residence times than in source regions with shorter residence times (40–45%). In addition, sediment profiles and near-bottom concentrations of butyltins are consistent with the rapid formation of MBT at the sediment-water interface. Simulated environmental degradation studies have found that tributyltin is not a highly persistent compound in freshwater and marine ecosystems under a wide range of environmental conditions.

The sediments are identified as the major environmental sink for tributyltin (TBT) in marine and estuarine systems. Observed distribution coefficients between sediments and the overlying water are in the approximate range from 0.2 to 20 1 g^-1. Higher values may reflect the presence of antifoulant paint chippings. Equilibrium partition coefficients (K _p ) for TBT with natural particulate material from laboratory experiments are reported in the range from 0.1 to 70 1 g^-1. The partition coefficient appears to decline with increasing particle concentration and to increase in proportion to organic carbon content, consistent with an organic carbon-water partition coefficient (K _oc ) of ~40 1 g^-1. Particle-water partitioning of TBT depends on salinity; both increases and decreases of K _p with salinity have been observed. The K _p is also shown to depend markedly on pH, and variations in this or other aspects of the chemical milieu could explain the varied relations to salinity. Published data indicate that the partitioning of TBT can show a Freundlich dependence on its own concentration, concentration on particles varying as about the two-thirds power of dissolved concentration in one particular case. A simplified exponential model of the uptake of contaminants into bodies of natural sediment is used to demonstrate the likely importance of the uptake and re-release of TBT in terms of its half-life in the sediments and its maximum rate of release to the water column. With rapid sediment exchange, re-release only exceeds a proportion ζ_μ of the previous input when the dimensionless product of TBT degradation rate and its residence time in the sediments with no degradation exceeds (1-ζ_μ)/ζ_μ. Example plots indicate conditions with maximum re-release >20% of the preceding input and half-life in the sediment exceeding 30 d.

Understanding the sorption behavior of tributyltin (TBT) is important for predicting its fate and effects in the aquatic environment. Equilibrium sorption coefficients ranging from 0.11 × 10³ to 350 × 10³ 1 kg^-1 have been measured in laboratory experiments using a wide variety of sorbent types, but the majority of the sorption coefficients are on the order of 10³ 1 kg^-1. Apparent sorption coefficients calculated from TBT concentrations measured in environmental sediments and overlying waters generally agree with laboratory measurements and are on the order of 10³ 1 kg^-1. Higher apparent sorption coefficients near boat maintenance facilities are probably the result of TBT-containing paint chips that are incorporated into sediments. Laboratory studies measuring the rate of TBT sorption or desorption show that the time required to reach equilibrium is relatively fast (hours) and that sorption is reversible. Longer-term (weeks to months) sorption kinetics for TBT have not been reported. For environments where mixing and water mass circulation times are slower than the equilibration process, laboratory-determined sorption coefficients may be reasonable estimates of TBT partitioning in the environment. Changes in salinity over the range encountered in estuaries can alter sorption coefficients, but these reported changes are varied and may depend on the particular system studied. Salinity effects may depend on sorbent-to-solution mass ratios used in equilibration experiments, and could arise from both the ionic and the hydrophobic components of the TBT molecule.

Tributyltin (TBT) has been analyzed in unfiltered water samples from the Chesapeake Bay (USA) from 1984 to 1989. Areas with large numbers of recreational vessels and one area with a high density of commercial and naval craft were targeted because of the likely input of TBT from these sources. The latter area also contained several large ship repair facilities that could contribute the antifouling agent. The range of TBT concentrations found at any one station was large with highest levels associated with times of peak usage. Concentrations in excess of 100 ng l^-1 were common in some areas. The state and federal restrictions on TBT use appear to have partially achieved their desired effect of reducing water concentrations. While only one data set is extensive enough to show statistically significant downward trends, all sets visually indicate a decrease. A model that fits the most extensive data set indicates an 8–30% per year decrease in water TBT concentration for stations near boating activities.

During the period of 1986 through 1989, tributyltin (TBT) levels in San Diego Bay (California, USA) surface waters averaged 4.7–13 ng l^-1 in the north bay, 1.3–9.9 ng l^-1 in the south bay, and 3.5–14 ng l^-1 in US Navy pier regions. TBT concentrations in the surface water of yacht harbors averaged 19–120 ng l^-1, while concentrations in bottom waters ranged from 8.8 to 61 ng l^-1. Yacht harbors and the naval pier regions showed a decline in TBT concentrations in water since restrictive paint-use legislation was enacted in January 1988. Average TBT concentrations in sediment in San Diego Bay ranged from 1.7 to 1100 ng g^-1 (dry weight) with higher values in yacht harbors adjacent to vessel repair and maintenance facilities. TBT concentrations in bottom water <60 ng l^-1 correlated well with concentrations in sediment. In regions where TBT levels in bottom waters were <30 ng l^-1, TBT levels in sediment were highly variable. TBT concentrations in sediment were generally highest in yacht harbors but did not exhibit significant temporal decreases coincident with restrictive legislation on TBT use. TBT burdens in tissues of the bay mussel (Mytilus edulus) in San Diego Bay ranged from 32 to 2100 ng g^-1 (wet wt); with bioaccumulation factors (BAF) ranging from 2.8 × 10³ to 6.6 × 10⁴. BAF decreased rapidly as TBT concentrations in surface water approached or exceeded 50 ng l^-1. In Pearl Harbor from 1986 through 1989, mean TBT levels in regional surface water ranged from 0.0 to 6.8 ng l^-1 in the channels; 0.0 to 4.9 ng l^-1 in the outlying regions; 2.4 to 31 ng l^-1 in Southeast Loch; and from 6.7 to 130 ng l^-1 in a small marina. Bottomwater samples throughout Pearl Harbor during this period averaged from 0.0 to 9.7 ng l^-1. TBT concentrations in surface water in Southeast Loch were highly correlated with the presence of TBT-coated ships, while no significant relationship was found between TBT concentrations in surface and bottom water in Pearl Harbor. Water samples from Honolulu harbors averaged 4.8–580 ng l^-1 in TBT concentration at the surface and 2.6–170 ng l^-1 at the bottom during this same period. Regional mean concentrations of TBT in Pearl Harbor sediments ranged from 10 to 4500 ng g^-1 (dry wt) and were highest near ship maintenance activities. On an average basis, the sediments from the Honolulu Harbor drydock facility contained three times the amounts of TBT as seen in comparable Pearl Harbor locations. Average TBT concentrations in oyster tissues from Hawaiian waters ranged from 41 to 1000 ng g^-1 (wet wt), and were directly proportional to ambient surfacewater concentrations. Oysters in Hawaiian waters accumulated TBT at rates of 8.6 × 10³–7.0 × 10⁴ times. Bioaccumulation factors in oyster tissue were inversely proportional to the concentration of TBT in ambient surface waters and decreased rapidly as TBT concentrations in surface water rose.

This chapter is a summary of investigations of the occurrence of tributyltin (TBT) and its less toxic degradation products in water and sediment in Canada in the period 1980–1985. Tributyltin was mainly found in areas of heavy boating or shipping traffic, which was consistent with its use as an antifouling agent. In 8% of the 269 locations across Canada at which samples were collected, TBT was found in water at concentrations that could cause chronic toxicity in a sensitive species, rainbow trout. Tributyltin was occasionally found in the surface microlayer of fresh water at much higher concentrations than in subsurface water. It was also found in 30% of sediment samples collected across Canada. The few fish analyzed that contained TBT were from harbors, a finding consistent with findings in water and sediment.

This chapter reports the results of monitoring environmental concentrations of tributyltin (TBT) in the United Kingdom from 1986 to 1988. The UK government implemented legislation in 1986, that limited the amount of tin in copolymer and free-association tributyltin-based antifouling paints. This was followed in 1987 by a ban on the use of TBT-based paints on boats under 25 m in length and on mariculture equipment. Concentrations of TBT have been monitored in seawater and sediments from estuaries that have traditionally supported shellfisheries and are popular centers of boating activity. By 1988, concentrations of TBT in water samples taken close to sites of oyster and mussel cultivation were approximately half of the concentrations recorded in 1986. However, at all of these sites in 1988 the concentrations of TBT in the water exceeded 2 ng l^-1, which is the environmental quality standard (EQS) set by the United Kingdom for the protection of marine life. The concentrations in many areas were above the toxicological threshold values of a variety of species. Water samples from marinas have also been analyzed, and in some cases concentrations of TBT in excess of 1000 ng l^-1 have been recorded; however, by 1988, concentrations of TBT in the water of several marinas had decreased to approximately a quarter of the values recorded in 1986. The concentrations of TBT in sediments were highest in samples taken close to high-density boat moorings or in marinas. Such samples contained concentrations of TBT >1 µg g^-1 (dry weight). Water samples have also been taken from commercial harbors, major waterways, and close to anchorages. It is difficult to assess the contribution of shipping to the inputs of TBT to the environment, when ships share the same body of water with small boats and yachts. However, the hosing-down of ships in dry-dock has been identified as a major source of input of TBT to the aquatic environment. Concentrations of TBT in major rivers, lakes, and the Norfolk Broads have been recorded. Levels of TBT in excess of 1000 ng l^-1 have been measured in samples from some freshwater marinas and boatyards. The spillage of timber-treatment chemicals, containing TBT, from riverside storage facilities, has sometimes been the cause of major inputs of TBT to the freshwater environment. The distribution of organotin (tributyltin and dibutyltin) throughout the water column has been investigated. Maximum concentrations occur in the surface microlayer and minimum values near the bottom. Concentrations in samples from the surface microlayer, taken with a Garrett screen sampler, were as much as 27 times greater than those in subsurface waters. It is probable that such high concentrations in the surface microlayer may have deleterious effects on both the neuston and on organisms of the littoral zone.

Direct entry of tributyltin (TBT) into the aquatic environment is primarily due to its use in antifouling paints on boats, which gives rise to contamination of waters and sediments of marinas, lakes, and coastal areas. To date, there is a lack of knowledge on other organotin sources and on the contamination of other environmental compartments. Inputs from wastewater and sewage sludge as well as from landfills are not well known. As the consumption of TBT and other organotins increases, these compounds are of growing importance in wastewater and sewage sludge. This chapter reviews speciation and contamination of wastewater and sludge, and describes the fate of organotins in a treatment plant. Organotins were determined by capillary gas chromatography with flame photometric detection after extraction and derivatization. In untreated wastewater of the city of Zurich, Switzerland, substantial concentrations of butyltins were determined. Phenyltins, dioctyltin, and tricyclohexyltin were not detected. Average values on six sampling days were 245 ng l^-1 monobutyltin (MBT), 523 ng l^-1 dibutyltin (DBT), and 157 ng l^-1 TBT. The mean daily load of organotin was 122 g. Partitioning in wastewater showed that ~90% of the butyltins was associated with suspended solids in the influent, and then the percentage dropped at each successive stage of the treatment process. As a consequence, these compounds are removed from raw wastewater by sedimentation in the primary clarifier. Aerobic digestion did not lead to a significant elimination from wastewater, and anaerobic digestion was not very effective in reducing organotins in sludge; hence, substantial organotin levels were determined in digested sludge. Average concentrations were 0.78 mg kg^-1 MBT, 0.98 mg kg^-1 DBT, and 0.99 mg kg^-1 TBT (dry weight). Organotins are therefore efficiently removed from wastewater (elimination 90%), but they become enriched in sewage sludge (daily load 59 g d^-1). Sludge is disposed of in landfills and at sea and is used in agriculture as a soil amendment to a large extent, giving a transfer path into the aquatic and terrestrial environment unrecognized thus far. Mono-, di-, and tributyltin residues have also been determined in the leachate of a landfill where the total butyltin concentration was 373 ng l^-1. The environmental input from landfills, however, is not as important as that from untreated wastewater and sewage sludge.

This chapter identifies, delineates, and prioritizes research information requirements relative to the environmental ramifications associated with organotin compounds. The lack of appropriate priorities for strategic planning and managing research has been a serious problem for the evaluation of highly toxic organotin compounds. Degrees of scientific uncertainty have always reduced or eroded the confidence of policy and decision makers. This uncertainty points to the necessity for improved and standardized risk characterization protocols, which need to be developed to improve ecological risk assessment and management. The focus of future requirements for long-term research information for organotin compounds should be on (1) quantification of the sources and loading levels of TBT in the environment; (2) delineation of the dispersion rates, processes, and transport mechanism; (3) characterization of the exposure pathways to selective target organisms of high risk; (4) assessment of the factors influencing bioavailability and biological uptake mechanisms; (5) identification and characterization of degradation rates and metabolic pathways; (6) quantification of relationships between laboratory studies of cause and effects, and effects found in the field; (7) development of rapid and inexpensive low-level advanced analytical protocols; (8) numerical modeling and prediction of ecosystem concentrations; (9) development of standard reference materials; and (10) risk assessment protocols.