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1999 | Buch

Atmospheric Transport of Pesticides: Assessing Environmental Risks Kapitel lesen Erstes Kapitel lesen

Fate of Pesticides in the Atmosphere: Implications for Environmental Risk Assessment

Proceedings of a workshop organised by The Health Council of the Netherlands, held in Driebergen, The Netherlands, April 22–24, 1998

herausgegeben von: Harrie F. G. Van Dijk, W. Addo J. Van Pul, Pim De Voogt

Verlag: Springer Netherlands

Enthalten in: Professional Book Archive

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Über dieses Buch

Global pesticide use is currently estimated at approximately 2. 5 billion kg per year (Pimentel eta/. , 1998). To be effective, pesticides need to persist for a certain period of time. However, the longer their persistence, the greater the potential for transport of a fraction of the amount applied away from the target area. Pesticides are dispersed in the environment by water currents, wind, or biota. Pesticides can directly contaminate ground and surface waters by leaching, surface run-off and drift. Pesticides can also enter the atmosphere during application by evaporation and drift of small spray droplets, that remain airborne. Following application, pesticides may volatilise from the crop or the soil. Finally, wind erosion can cause soil particles and dust loaded with pesticides to enter the atmosphere. The extent to which pesticides enter the air compartment is dependent upon many factors: the properties of the substance in question (e. g. vapour pressure), the amount used, the method of application, the formulation, the weather conditions (such as wind speed, temperature, humidity), the nature of the crop and soil characteristics. Measurements at application sites reveal that sometimes more than half of the amount applied is lost into the atmosphere within a few days (Spencer and Cliath, 1990; Taylor and Spencer; 1990; Van den Berg et a/. , this issue).

Inhaltsverzeichnis

Frontmatter
Atmospheric Transport of Pesticides: Assessing Environmental Risks
Abstract
Current global food requirements have made great demands on agricultural production, including the need for efficient weed and pest control. In the second half of the 20th century, this had led to an ever increasing use of pesticides. Pesticides are a special case inasmuch as they are applied directly in the environment for the purpose of eliminating pests. Due to their obvious inherent toxicity, strict regulations exist throughout the world regarding their registration.
H. F. G. van Dijk, W. A. J. van Pul, P. de Voogt
Environmental Risk Assessment for Pesticides in the Atmosphere; the Results of an International Workshop
Abstract
The Health Council of the Netherlands organised an international workshop on the fate of pesticides in the atmosphere and possible approaches for their regulatory environmental risk assessment. Approximately forty experts discussed what is currently known about the atmospheric fate of pesticides and major gaps in our understanding were identified. They favoured a tiered approach for assessing the environmental risks of atmospheric dispersion of these chemicals. In the first tier a pesticide’s potential for emission during application, as well as its volatilisation potential should be assessed. Estimates of the former should be based on the application method and the formulation, estimates of the latter on a compound’s solubility in water, saturated vapour pressure and octanol/water partition coefficient. Where a pesticide’s potential for becoming airborne exceeds critical values, it should be subjected to a more rigorous second tier evaluation which considers its toxicity to organisms in non-target areas. This evaluation can be achieved by calculating and comparing a predicted environmental concentration (PEC) and a predicted no-effect concentration (PNEC). By applying an extra uncertainty factor the PNEC can be provisionally derived from standard toxicity data that is already required for the registration of pesticides. Depending on the distance between the source and the reception area, the PEC can be estimated for remote areas using simple dispersion, trajectory type models and for nearby areas using common dispersion models and standard scenarios of pesticide use. A pesticide’s atmospheric transport potential is based on factors such as its reaction rate with OH radicals. It should be used to discriminate between those compounds for which only the risks to nearby ecosystems have to be assessed, and those for which the risks to remote ecosystems also have to be determined. The participants were of the opinion that this approach is, in principle, scientifically feasible, although the remaining uncertainties are substantial. Further field and laboratory research is necessary to gain more reliable estimates of the physico-chemical properties of pesticides, to validate and improve environmental fate models and to validate the applicability of standard toxicity data. This will increase both the accuracy of and our confidence in the outcome of the risk assessment.
Robert Guicherit, Dick J. Bakker, Pim De Voogt, Frederik Van Den Berg, Harrie F. G. Van Dijk, W. Addo J. Van Pul
Atmospheric Dispersion of Current-Use Pesticides: A Review of the Evidence from Monitoring Studies
Abstract
Recently, evidence has accumulated that the extensive use of modern pesticides results in their presence in the atmosphere at many places throughout the world. In Europe over 80 current-use pesticides have been detected in rain and 30 in air. Similar observations have been made in North America. The compounds most often looked for and detected are the organochlorine insecticide lindane and triazine herbicides, especially atrazine. However, acetanilide and phenoxyacid herbicides, as well as organophosphorus insecticides have also frequently been found in rain and air. Concentrations in air normally range from a few pg/m3 to many ng/m3. Concentrations in rain generally range from a few ng/L to several μg/L. In fog even higher concentrations are observed. Deposition varies between a few mg/ha/y and more than 1 g/ha/y per compound. However, these estimates are usually based on the collection and analysis of (bulk) precipitation and do not include dry particle deposition and gas exchange. Nevertheless, model calculations, analysis of plant tissue, and first attempts to measure dry deposition in a more representative way, all indicate that total atmospheric deposition probably does not normally exceed a few g/ha/y. So far, little attention has been paid to the presence of transformation products of modern pesticides in the atmosphere, with the exception of those of triazine herbicides, which have been looked for and found frequently.
Generally, current-use pesticides are only detected at elevated concentrations in air and rain during the application season. The less volatile and more persistent ones, such as lindane, but to some extent also triazines, are present in the atmosphere in low concentrations throughout the year. In agricultural areas, the presence of modern pesticides in the atmosphere can be explained by the crops grown and pesticides used on them. They are also found in the air and rain in areas where they are not used, sometimes even in remote places, just like their organochlorine predecessors. Concentrations and levels are generally much lower there. These data suggest that current-use pesticides can be transported through the atmosphere over distances of tens to hundreds, and sometimes even more than a thousand kilometres. The relative importance of these atmospheric inputs varies greatly. For mountainous areas and remote lakes and seas, the atmosphere may constitute the sole route of contamination by pesticides. In coastal waters, on the other hand, riverine inputs may prevail. To date, little is known about the ecological significance of these aerial inputs.
Harrie F. G. Van Dijk, Robert Guicherit
Ecotoxicological Risk Assessment of Pesticides Subject to Long-Range Transport
Abstract
Concern has arisen about the possible ecological effects of persistent pesticides that become airborne during or after application and are transported to regions far away from where they were applied. In this paper an ecotoxicological approach is outlined that may support assessments of products suspected of long-range transport capacity. It is proposed that the risk is estimated from a classical PNEC/PEC comparison for the surface layer of a remote area, where PEC is estimated from dose rate, emission factors, atmospheric residence time and persistence, while PNEC is estimated from ecotoxicological information collected as part of the registration procedure. According to this “null model”, risk assessment of pesticides subject to long-range transport is not different from the usual risk assessment, provided that due attention is paid to losses occurring during transport and accumulation in remote areas with low temperature. A simplified equation is derived for estimating PEC from the recommended dose rate, which shows that the concentration in the remote area is higher than in the target area only if its residence time is at least two ordes of magnitude longer than the corresponding value in the target area. A review of ecotoxicity data for effects of volatile pesticides on arthropods indicates that effect levels in the air compartment are far above the concentrations of concern in long-range transport. Arguments supporting the view that remote areas, specifically the polar regions, are characterized by ecosystems that are more vulnerable than the ones on which the usual risk assessment is based, are reviewed. Although residues of organochlorines are of concern, there does not seem to be concrete epidemiological or experimental evidence about effects of modern pesticides on wildlife in remote areas. It is concluded that there is no reason to reject the “null model” at the moment, however, in view of the large uncertainty involved, it is proposed that the maximum acceptable ratio between PNEC and PEC be increased by an extra safety factor.
Nico M. van Straalen, Cornelis A. M. van Gestel
Micrometeorologic Methods for Measuring the Post-Application Volatilization of Pesticides
Abstract
A wide variety of micrometeorological measurement methods can be used to estimate the postapplication volatilization of pesticides from treated fields. All these estimation methods require that the entire study area have the same surficial characteristics, including the area surrounding the actual study site, and that the pesticide under investigation be applied as quickly and as uniformly as possible before any measurements are made. Methods such as aerodynamic profile, energy balance, eddy correlation, and relaxed eddy accumulation require a large (typically 1 or more hectare) study area so that the flux measurements can be made in a well developed atmospheric boundary-layer and that steady-state conditions exist. The area surrounding the study plot should have similar surficial characteristics as the study plot with sufficient upwind extent so the wind speed and temperature gradients are fully developed. Mass balance methods such as integrated horizontal flux and trajectory simulations do not require a large source area, but the area surrounding the study plot should have similar surficial characteristics.
None of the micrometeorological techniques for estimating the postapplication volatilization fluxes of pesticides disturb the environment or the soil processes that influence the gas exchange from the surface to the atmosphere. They allow for continuous measurements and provide a temporally averaged flux value over a large area. If the behavior of volatilizing pesticides and the importance of the volatilization process in redistributing pesticides in the environment are to be fully understood, it is critical that we understand not only the processes that govern pesticide entry into the lower atmosphere, but also how much of the millions of kilograms of pesticides that are applied annually are introduced into, and redistributed by, the atmosphere. We also must be aware of the assumptions and limitations of the estimation techniques used, and adapt the field of pesticide volatilization flux measurements to advances in atmospheric science.
M. S. Majewski
Atmospheric Transport and Air-Surface Exchange of Pesticides
Abstract
Atmospheric transport and exchange of pesticides with soil, vegetation, water and atmospheric particles are discussed, with an emphasis on applying physicochemical properties of the compound to describe environmental partitioning. The octanol-air partition coefficient is promoted as a unifying property for describing volatilization of pesticides from soil and sorption to aerosols. Present-day sources of organochlorine (OC) pesticides to the atmosphere are continued usage in certain countries and volatilization from contaminated soils where they were used in the past. Models are available to predict volatilization from soil; however, their implementation is hampered by lack of soil residue data on a regional scale. The need to differentiate “new” and “old” sources is increasing, as countries negotiate international controls on persistent organic pollutants (POPs). A new technique, based on the analysis of individual pesticide enantiomers, is proposed to follow emission of chiral OC pesticides from soil and water. Air monitoring programs in the Arctic show the ubiquitous presence of OC pesticides, PCBs and other POPs, and recently a few “modern” pesticides have been identified in fog and surface seawater. Atmospheric loadings of POPs to oceans and large lakes take place mainly by air-water gas exchange. In the case of OC pesticides and PCBs, aquatic systems are often near air-water equilibrium or even oversaturated. Measurement of water/air fugacity ratios suggests revolatilization of PCBs and several OC pesticides in the Great Lakes and, for αhexachlorocyclohexane (α-HCH), in the Arctic Ocean. Outgassing of α-HCH in large lakes and arctic waters has been confirmed by enantiomeric tracer studies. The potential for pesticides to be atmospherically transported depends on their ability to be mobilized into air and the removal processes that take place enroute: wet and dry deposition of gases and particles and chemical reactions in the atmosphere. Measurement of reaction rate constants for pesticides in the gas and particle phase at a range of environmental temperatures is a critical research need. The transport distance of a chemical is related to its overall environmental persistence, determined by the partitioning among different compartments (water, sediment, soil, air), degradation rates in each compartment and mode of emission (into water, soil, air). Several pesticides found in the arctic environment have predicted lifetimes in the gas phase of only a few days in temperate climates, pointing out the need for monitoring and evaluation of persistence in cold regions.
Terry F. Bidleman
Modelling of Atmospheric Transport and Deposition of Pesticides
Abstract
Modelling of atmospheric transport and deposition of pesticides is presented and discussed. Modelling on regional scale builds on the existing knowledge gained in other air pollution fields. An overview of current modelling studies on transport and deposition on a regional scale (typically 30–3000 km) is given. From these studies it is concluded that the models are capable in simulating the spatial distribution of the concentrations and depositions. However, large uncertainties are present in this type of modelling and are for the greater part induced by the uncertainty in the emissions and subsequently in the exchange process parameterisations and the physicochemical properties needed in the parameterisations. Many more measurement data are needed to validate the models.
J. Hans A. Van Jaarsveld, W. Addo J. Van Pul
Regulatory Risk Assessment of Pesticide Residues in Air
Abstract
Background information describing current approaches taken by different countries to risk assessment in regard of pesticide residues in air is presented with a view to stimulating discussion of the subject in order to identify means for improving both the underlying science and administrative procedures concerned. Fundamental regulatory objectives are explored, alternative guidelines for conduct of exposure evaluation, risk assessment and regulatory decision making are examined and the basic components of the technical framework in which this complex work is carried out are discussed. The criteria which are capable of being used for regulatory decision support are considered with a view to questioning their feasibility for practical use and relevance for operation to provide a robust basis for regulatory risk assessment for plant protection products. Brief recommendations are given for aspects of discussion where attention should be focused.
A. J. Gilbert
Emission of Pesticides into the Air
Abstract
During and after the application of a pesticide in agriculture, a substantial fraction of the dosage may enter the atmosphere and be transported over varying distances downwind of the target. The rate and extent of the emission during application, predominantly as spray particle drift, depends primarily on the application method (equipment and technique), the formulation and environmental conditions, whereas the emission after application depends primarily on the properties of the pesticide, soils, crops and environmental conditions. The fraction of the dosage that misses the target area may be high in some cases and more experimental data on this loss term are needed for various application types and weather conditions. Such data are necessary to test spray drift models, and for further model development and verification as well. Following application, the emission of soil fumigants and soil incorporated pesticides into the air can be measured and computed with reasonable accuracy, but further model development is needed to improve the reliability of the model predictions. For soil surface applied pesticides reliable measurement methods are available, but there is not yet a reliable model. Further model development is required which must be verified by field experiments. Few data are available on pesticide volatilization from plants and more field experiments are also needed to study the fate processes on the plants. Once this information is available, a model needs to be developed to predict the volatilization of pesticides from plants, which, again, should be verified with field measurements. For regional emission estimates, a link between data on the temporal and spatial pesticide use and a geographical information system for crops and soils with their characteristics is needed.
F. Van Den Berg, R. Kubiak, W. G. Benjey, M. S. Majewski, S. R. Yates, G. L. Reeves, J. H. Smelt, A. M. A. Van Der Linden
Transformations of Pesticides in the Atmosphere: A State of the Art
Abstract
The current knowledge about transformation rates and products of pesticides in the atmosphere is reviewed. Reactive species and their concentrations in the atmosphere are presented. Reactions of pesticides with these species (including photolysis) in the gas and the particulate phase are evaluated from available experimental data. The potential of estimation methods is discussed. Experimental techniques for laboratory and outdoor measurements are reviewed. Finally, an estimation is made of uncertainties in atmospheric lifetimes due to chemical or physical reactions. It is concluded that the most important transformation of pesticides in the atmosphere is due to reaction with OH radicals. Very few experimental data for pesticides are available though. The levels of uncertainty in OH radical concentrations are acceptable, however, for a proper estimation of atmospheric removal rates due to reactions with OH radicals of those pesticides for which experimental transformation rates (of homologues) are available.
Roger Atkinson, Rob Guicherit, Ronald A. Hites, Wolf-Ulrich Palm, James N. Seiber, Pim De Voogt
Atmospheric Transport and Deposition of Pesticides: An Assessment of Current Knowledge
Abstract
The current knowledge on atmospheric transport and deposition of pesticides is reviewed and discussed by a working group of experts during the Workshop on Fate of pesticides in the atmosphere; implications for risk assessment, held in Driebergen, the Netherlands, 22–24 April, 1998. In general there is a shortage of measurement data to evaluate the deposition and re-emission processes. It was concluded that the mechanisms of transport and dispersion of pesticides can be described similarly to those for other air pollution components and these mechanisms are rather well-known. Large uncertainties are present in the exchange processes at the interface between air and soil/water/vegetation. In all process descriptions the uncertainty in the physicochemical properties play an important role. Particularly those in the vapour pressure, Henry’s law constant and its temperature dependency. More accurate data on physicochemical properties and particularly the temperature dependencies is needed.
W. Addo J. Van Pul, Terry F. Bidleman, Eva Brorström-Lundén, Peter J. H. Builtjes, Sergey Dutchak, Jan H. Duyzer, Sven-Erik Gryning, Kevin C. Jones, Harrie F. G. Van Dijk, J. Hans A. Van Jaarsveld
Implementing Atmospheric Fate in Regulatory Risk Assessment of Pesticides: (How) Can it be Done?
Abstract
Atmospheric fate of pesticides and their possible effects in ecosystems beyond the immediate surrounding of the application site are not actively considered in currently used regulatory risk assessment schemes. Concern with respect to atmospheric transport and subsequent deposition of pesticides in non-target areas is however growing. In this article the results of discussions on the possibilities of implementing atmospheric fate in regulatory risk assessment are presented. It is concluded that implementing atmospheric fate in regulatory risk assessment schemes is possible and that, from a scientific point of view, these schemes should distinguish between pesticides on the basis of both their possibility/probability to reach non-target areas and on their toxicity. This implies that application of the precautionary principle or use of intrinsic pesticide properties alone is not considered justifiable. It is recommended that the risk assessment scheme should follow a tiered approach. The first tier should be entered only if the existing regulatory risk assessment procedure, including a local PEC:PNEC calculation, has been passed and involves a test for the pesticide’s total atmospheric emission potential, i.e.its potential for becoming airborne during and after application. The second tier, which is only entered if the total emission potential is higher than a certain trigger value, should consist of a PEC:PNEC calculation for regional off-site areas (10–50 km) (tier 2A). If the pesticide’s atmospheric transport potential is expected to exceed a certain value, the PEC:PNEC ratio should also be calculated for more remote areas (>1000 km) (tier 2B).
D. J. Bakker, A. J. Gilbert, D. Gottschild, T. Kuchnicki, R. W. P. M. Laane, J. B. H. J. Linders, D. Van De Meent, M. H. M. M. Montforts, J. Pino, J. W. Pol, N. M. Van Straalen
Backmatter
Metadaten
Titel
Fate of Pesticides in the Atmosphere: Implications for Environmental Risk Assessment
herausgegeben von
Harrie F. G. Van Dijk
W. Addo J. Van Pul
Pim De Voogt
Copyright-Jahr
1999
Verlag
Springer Netherlands
Electronic ISBN
978-94-017-1536-2
Print ISBN
978-90-481-5329-9
DOI
https://doi.org/10.1007/978-94-017-1536-2