Reviews of Environmental Contamination and Toxicology Volume 237

Caenorhabditis elegans is a nematode widely used as a toxicological model. The transparency of its body, short lifespan, ability to self-fertilize and ease of culture are advantages that make it ideal as a model in toxicology. Due to the fact that some of its biochemical pathways are similar to those of humans, it has been employed in research in several fields. Its use in environmental toxicological assessments allows the determination of multiple endpoints such as lethality, growth, reproduction, and locomotion. Other endpoints use reporter genes, such as GFP, driven by regulatory sequences from genes modulated by different toxicity pathways, such as heat shock responses, oxidative stress, xenobiotic metabolism, and metallothioneins production, among others. C. elegans has allowed the evaluation of neurotoxic effects for heavy metals and pesticides, among those more frequently studied, as the nematode has a very well defined nervous system. More recently, nanoparticles are emergent pollutants whose toxicity can be explored using this nematode. Overall, almost every type of known toxicant has been tested with this animal model. In the near future, the available knowledge on the life cycle of C. elegans should allow more studies on reproduction and transgenerational toxicity for newly developed chemicals and materials, as a powerful tool to protect human health.

The literature research conducted and the data presented here focus on heavy metals concentrations in sediment and pore water, however other inorganics are considered. The importance of minimizing atmospheric exposure during sample collection and processing to minimize the effects of geochemical changes is clear. The authors propose that with these considerations in mind pore water data should be evaluated by considering the bioavailability of metals, the partitioning of contaminants between the aqueous and solid phases and comparing these concentrations to Interstitial Water Toxicity Units/Interstitial Water Benchmark Units.

The insecticide dimethoate, an organophosphate, was first introduced in 1962 for broad spectrum control of a wide range of insects including mites, flies, aphids, and plant hoppers. It is known to inhibit AChE activity like other organophosphates, resulting in nerve damage which may lead to death. In the environment, hydrolysis represents a major degradation pathway under alkaline conditions, whereas volatilization is not a major route of dissipation from either water or moist soils. Dimethoate is also degraded by microbes under anaerobic conditions and the major degradation product, omethoate, has been identified. Dimethoate has been found to adversely impact many organisms. In plants, photosynthesis and growth are highly impacted, whereas birds exhibit inhibition in brain enzyme activity, thus sublethal effects are apparent. Aquatic organisms are expected to be highly impacted via direct exposure and display changes in swimming behavior.

Crystal Violet (CV), a triphenylmethane dye, has been extensively used in human and veterinary medicine as a biological stain, as a textile dye in textile processing industries and also used to provide a deep violet color to paints and printing ink. CV is also used as a mutagenic and bacteriostatic agent in medical solutions and antimicrobial agent to prevent the fungal growth in poultry feed. Inspite of its many uses, CV has been reported as a recalcitrant dye molecule that persists in environment for a long period of time and pose toxic effects. It acts as a mitotic poison, potent carcinogen and a potent clastogene promoting tumor growth in some species of fish. Thus, CV is regarded as a biohazard substance. Although, there are several physico-chemical methods such as adsorption, coagulation and ion-pair extraction reported for the removal of CV, but these methods are insufficient for the complete removal of CV from industrial wastewaters and also produce large quantity of sludge containing secondary pollutants. However, biological methods are regarded as cost-effective and eco-friendly for the treatment of industrial wastewaters, but these methods also have certain limitations. Therefore, there is an urgent need to develop such eco-friendly and cost-effective biological treatment methods, which can effectively remove the dye from industrial wastewaters for the safety of environment, as well as human and animal health.

The aim of this revision was to build an updated collection of information focused on the mechanisms and elements involved in metabolic pathways of aromatic hydrocarbons by bacteria. Enzymes as an expression of the genetic load and the type of electron acceptor available, as an environmental factor, were highlighted. In general, the review showed that both aerobic routes and anaerobic routes for the degradation of aromatic hydrocarbons are divided into two pathways. The first, named the upper pathways, from the original compound to central intermediate compounds still containing the aromatic ring but with the benzene nucleus chemically destabilized. The second, named the lower pathway, begins with ring de-aromatização and subsequent cleavage, resulting in metabolites that can be used by bacteria in the production of biomass. Under anaerobic conditions the five mechanisms of activation of the benzene ring described show the diversity of chemical reactions that take place. Obtaining carbon and energy from an aromatic hydrocarbon molecule is a process that exhibits the high complexity level of the metabolic apparatus of anaerobic microorganisms. The ability of these bacteria to express enzymes that catalyze reactions, known only in non-biological conditions, using final electron acceptors with a low redox potential, is a most interesting topic. The discovery of phylogenetic and functional characteristics of cultivable and non-cultivable hydrocarbon degrading bacteria has been made possible by improvements in molecular research techniques such as SIP (stable isotope probing) making trace of ¹³C, ¹⁵N and ¹⁸O into nucleic acids and proteins.

There are multiple sources of lead in the environment. However, scientific evidence points to spent lead ammunition as the most frequent cause of lead exposure and poisoning in scavenging birds in the United States. Despite the ban on its use for waterfowl hunting, lead ammunition is still widely used for other hunting and shooting activities. Therefore, it can remain on the landscape in carcasses not retrieved and in discarded offal piles. Carcasses and gut piles can be attractive food sources to scavenging birds that can ingest bullet fragments or shot while feeding. Scavenging birds may be particularly vulnerable to exposure and effects of lead due to their foraging strategies and food preferences, physiological processes that facilitate the absorption of lead, and demographic traits. Numerous lines of evidence support ammunition as the source of exposure in the majority of lead poisoned scavenging birds and include the recovery of ingested lead fragments or shot from exposed birds, observations of birds feeding on contaminated carcasses, isotopic signatures of lead in tissue that match that found in ammunition, patterns of mortality coincident with hunting seasons, and the lack of abundant evidence for other lead sources. Lead can be replaced in ammunition by alternative metals that are currently available and present limited environmental threats.