Ecological Impacts of Toxic Chemicals

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Modern living standards depend largely on the production and usage of thousands of chemicals, many of which are toxic and synthetically produced. These substances are discharged into the air, soil, water bodies and the sea through a variety of ways, becoming pollutants of our environment. The investigation of their fate and impacts they have on ecosystems is called ecotoxicology, a multidisciplinary science which intends to evaluate the nature of the discharge, the transformation and distribution of toxicants in the environment, exposure, lethality and sublethal effects on organisms, population responses, and changes in community structure and ecosystem function. The sources and mode of action of some of the most common groups of toxicants are described in this chapter, leaving their fate and effects in organisms and ecosystems for the subsequent chapters.

Release of toxic chemicals into the environment cannot always be avoided completely. As a result organisms, man included, will be exposed to chemicals via the environment. Given the release of certain chemicals into the environment, their exposure concentrations in air, water and soil would depend on the rates at which they are removed from the environment. This chapter deals with the transport and transformation processes that affect concentrations in the environment, with emphasis on the modeller's perspective. Being interested primarily in the effects that processes have on concentrations of chemicals in environmental media, we focus on a quantitative description of the rates at which losses from the environment take place, and on how these rates differ for different chemicals. We systematically formulate process rate constants for each transport or transformation process. Eventually, the rate constants combine into a mass balance model which allows us to describe and predict how releases into the environment result in exposure concentrations of organisms.

Metals and metalloids are elemental substances that occur naturally in the Earth's crust, and are variously incorporated into biological systems as structural components or proteins. Imbalances in the environmental concentrations of several metals present a challenge to ecosystems because the species that form part of these ecosystems are often not equipped to regulate internal concentrations of these elements, or employ detoxification mechanisms that serve to biomagnify these elements in the food chain. This review examines the trophic movement of metals and metalloids within terrestrial ecosystems and the consequences of biomagnification and toxicity on populations. Several elemental contaminants are given special emphasis, including copper, zinc, arsenic, selenium, molybdenum, cadmium, mercury and lead. All these elements are of high historical importance and continue to be deposited within the biosphere.

Pesticides are toxic chemicals used to control pests, weeds and pathogens. Three quarters of all pesticides are employed in agricultural production, particularly in developed countries, in an effort to mitigate crop damage endured by intensive agriculture. However, after more than 60 years of worldwide usage, their side-effects on terrestrial ecosystems – even when applied as recommended – are obvious. This chapter examines the ecological problems caused by specific chemicals/groups, so that this awareness may help improve agricultural practices through appropriate risk management. Fungicides alter the microbial-fungi communities responsible for the recycling of nutrients in the soil, and copper fungicides are toxic to earthworms and other animals. The routine application of herbicides has produced a net loss of plant biomass and biodiversity in many landscapes, which indirectly reduces the associated arthropod communities and leads to population declines in many species of birds, and possibly amphibians too, due to lack of food. Insecticides are very toxic to most invertebrates in the soil, birds and small mammals, causing significant reductions in their populations and disturbing the trophic structure of their communities. Persistent pesticides accumulate in soil and concentrate through the trophic chain, causing a plethora of sublethal effects which are negative for the survival of individuals as well as the viability of their populations; the long term effects of DDT and cyclodiene poisoning in birds is still an ecological issue despite more than 30 years of not being applied in most developed countries. While pesticides have increased our agricultural productivity and helped feed the current human population, the price of this productivity is being paid by the Earth's ecosystems at large.

Assessing the potential for ecological impacts of pesticides requires a hierarchical approach with research ranging from simple laboratory to complex field experiments and operational monitoring. While all levels of study provide useful information, higher tier research has inherently greater environmental relevance and inference potential. In this chapter, selected higher tier studies relating to the use of herbicides glyphosate and triclopyr, as well as the insecticides Bacillus thuringiensis var. kurstaki (Btk) and diflubenzuron in the forest sector are reviewed. These case examples illustrate scenarios in which higher tier studies either negate or support the presumptions of risk derived from results of lower tier experiments. Specifically, assessment of the cases for glyphosate and Btk support their continued judicious use as environmentally acceptable components of integrated vegetation and insect pest management strategies. In contrast, higher level studies confirm risk postulates associated with typical forest-sector use patterns for triclopyr ester and diflubenzuron. Mitigation measures are required to ensure that use of these latter compounds do not pose undue risk to sensitive non-target organisms. In a broader context, the ecological implications of pesticide use in the forest sector must be considered in light of the fact that any management action, including the “no intervention” option, carries both economic and ecological risk. Strict adherence to the weight of scientific evidence principle, incorporation of knowledge gained from all levels of investigation, and a balanced assessment of relative risks of all potential options are considered primary requisites of comprehensive risk analysis and effective decision making.

Pesticides can enter surface waters via different routes, among which runoff driven by precipitation or irrigation is the most important in terms of peak concentrations. The exposure can cause direct effects on all levels of biological organisation, while the toxicant mode of action largely determines which group of organisms (primary producers, microorganisms, invertebrates or fish) is affected. Due to the interconnectedness of freshwater communities, direct effects can entail several indirect effects that are categorised and discussed. The duration of effects depends on the recovery potential of the affected organisms, which is determined by several key factors. Long-term effects of pesticides have been shown to occur in the field. However, the extent of the effects is currently uncertain, mainly because of a lack of large-scale data on pesticide peak concentrations. In the final section, we elucidate the different approaches to predict effects of pesticides on freshwater ecosystems. Various techniques and approaches from the individual level to the ecosystem level are available. When used complementary they allow for a relatively accurate prediction of effects on a broad scale, though the predictive strength is rather limited when it comes to the local scale. Further advances in the risk assessment of pesticides require the incorporation and extension of ecological knowledge.

The ecological impacts of organic pollutants on freshwater ecosystems have attracted immense scientific, regulatory, and public attention over the past fifty years. In part, this reflects the significant role that freshwater ecosystems play as a repository for anthropogenic chemicals relative to other systems. Some of the most severe ecological impacts have been documented in freshwater ecosystems from persistent organic pollutants (POPs) such as polychlorinated biphenyls, polychlorinated dioxins and furans, and polycyclic aromatic hydrocarbons. Such chemicals can reside for long periods in freshwater sediments, which can then constitute a continual source to the environment even when direct inputs have ceased. Exposure of freshwater biota at lower trophic levels to persistent chemicals can result in transfer to, and ecological impacts at, higher trophic levels through bioaccumulation and biomagnification. In contrast to historically significant organic pollutants, the pervasive nature of new pollutant classes (e.g. pharmaceuticals, polybrominated diphenyl ethers, and perfluorinated surfactants) in global freshwater ecosystems is beginning to be recognized but the full spectrum of their ecological impacts is poorly understood. In this chapter we review documented and potential ecological impacts of organic chemicals in freshwater ecosystems. We focus predominantly on effects at the population, community, and ecosystem levels but, to the extent that our understanding of impacts at these higher levels is predominantly extrapolated from information derived at lower levels, we also include information at the organism and sub-organism level. In addressing each chemical class, impacts on microbial, plant, invertebrate, fish, and fish-eating bird populations are considered where data exists.

In recent years, sources, types and levels of contaminants in the marine environment have increased as a consequence of anthropogenic activities worldwide. Chemical substances are usually present in the marine environment at different concentrations. They are accumulated in the tissues of marine organisms exerting damaging effects at different levels of organization, from organisms to communities and ecosystems. The understanding of their effects and distribution has increased substantially since the early reports on the biological effects of marine pollution and associated monitoring problems. This Chapter has been divided into five main sections: (i) molecular, cellular and tissue level biomarkers in assessing effects, reviewing the use of biomarkers in monitoring effects; (ii) biological effects at organism and population level; (iii) bioassay studies at organism level, focusing on ecotoxicology and discussing toxicity estimation and bioassay limitations; (iv) ecological effects at community level, including structural parameters, such as richness, diversity, etc., but also the proportion of opportunistic and sensitive species, discussing the multiple pressure interactions; and (v) measuring pollutant effects in integrative assessments, both in evaluating risk and assessing the ecological status of the ecosystems. The main objective of the Chapter is to bring together the knowledge on the biological effects of pollution, developed in recent years, at different biological levels of organization.

In this chapter we review the effects of anthropogenically derived chemical pollutants on tropical coral reef ecosystems. A wide range of compounds, including pesticides, trace metals and petroleum hydrocarbons enter reef systems through various pathways and affect different reef species and/or life history stages. Tools for evaluation of chemical stress on coral reefs consist of molecular, biochemical, physiological and ecological bioindicators, providing information at organismal or community levels. This chapter collates and assesses available information on different chemical stressors in the marine environment and the effects on reef-building corals. Ecological effects from chemical stressors are strongly dependent on exposure characteristics. Three probable pollution scenarios are discussed and their individual properties evaluated. Short-term, pulse-like pollution events including oil spills or antifoulant deposition through ship groundings often have a direct and severe impact upon multiple trophic levels of the system. However, these events are typically localised and possibly irrelevant on an ecosystem-wide scale. In contrast, recurring pollution events such as input from river floods or chronic pollution from land runoff (e.g. sewage treatment effluent or herbicides), may exert subtle effects on lower trophic levels of the system, affecting species fitness and driving adaptation. Effects from recurring or chronic pollution are more likely to combine and interact with other environmental factors, but remain poorly understood. Over time, chronic sub-lethal stress may decrease resilience of reef organisms to other forms of environmental stress like elevated sea surface temperatures and ocean acidification.

Most of the primary production of the world's oceans takes place in the water column, thereby fuelling not only marine pelagic food-webs, but also most benthic communities. In addition, nearly all marine organisms depend on the pelagic zone for some part of their life-cycle. Although most contaminants have physico-chemical properties that cause them to associate with organic material particles and eventually be transported to sediments, direct contaminant inputs are predominantly to pelagic ecosystems. Taking both the ecological importance and the contaminant load into account, there is a surprising lack of scientific knowledge concerning the effects of contaminants in pelagic systems. The main reasons are presumably the difficulty in linking exposure with processes at a scale relevant for environmental management, and challenges involved in using pelagic fish and zooplankton species for experimental studies (excluding the 2-3 copepod species used for regulatory toxicity testing). Contaminants have been shown to affect primary producers as well as secondary producers-consumers, but there is very limited knowledge about ecological impacts. Top predators in marine ecosystems (piscivorous fish species, marine mammals, seabirds) will be particularly at risk from persistent organic contaminants since they will biomagnify. Although there is evidence of effects caused by such substances in the past, there is a need for continuous updates including “new” contaminants. Most relevant for lower trophic levels, micro- and mesocosm studies under controlled conditions are critical for increased understanding of processes and putative effects of contaminants in the pelagic zone. Some field-based strategies have been suggested and implemented to varying degrees for environmental management of contaminants in the water column, including riskbased modelling, bioassay-analyses of environmental samples or extracts (e.g., through the use of passive samplers), caging of organisms and, finally, collection and analyses of native organisms.

Contamination of aquatic ecosystems is always of concern to environmental scientists; however, these systems also possess unique capabilities allowing them to eliminate or remediate certain levels of pollutants. Primarily through the presence of vegetation, aquatic ecosystems are known to be capable of removing or at least decreasing pollutant loads travelling through the aqueous phase. In addition to vegetation, soil/sediment and microbes play a significant role in transferring or transforming pollutants to acceptable levels in aquatic ecosystems. This chapter focuses on some of the primary literature describing phytoremediation of organic pollutants (e.g. hydrocarbons and pesticides) and inorganic pollutants (e.g. metals and nutrients). Research indicates the popularity and success of phytoremediation techniques used to clean up both organic and inorganic pollutants from the water column. While certain caution should always be exercised, phytoremediation continues to serve as a successful means of pollutant remediation in aquatic ecosystems.

Full Text Available.

Full Text Available.

Full Text Available.