Environmental toxicology is a multidisciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms. Ecotoxicology is a subdiscipline of environmental toxicology concerned with studying the harmful effects of toxicants at the population and ecosystem levels.
Research into ecotoxicology can be classified into three fundamental concerns: abiotic factors, which characterize the physicochemistry of environments; biotic factors, relating to biological structures and functions; and contamination factors, which define the modes of pollution of ecosystems. The most significant research methodologies currently being developed in aquatic ecotoxicology are presented, specifically experimental approaches in the laboratory
This text is divided into three parts. The first part describes basic toxicological concepts and methodologies used in aquatic toxicity testing, including the philosophies underlying testing strategies now required to meet and support regulatory standards. The second part of the book discusses various factors that affect transport, transformation, ultimate distribution, and accumulation of chemicals in the aquatic environment, along with the use of modelling to predict fate.; The final section of the book reviews types of effects or endpoints evaluated in field studies and the use of structure-activity relationships in aquatic toxicology to predict biological activity and physio-chemical properties of a chemical. This section also contains an extensive background of environmental legislation in the USA and within the European Community, and an introduction to hazard/risk assessment with case studies.
This chapter provides an overview of the basic concepts and methods of study used in environmental epidemiology. One approach that epidemiologists take to identify factors that cause or influence disease occurrence is to evaluate time, person, and place characteristics. Diseases which result in mortality are of considerable interest for public health assessment because of the suffering and cost associated with death, particularly when it occurs at a young age. Measurement of exposure is a component of epidemiologic studies in which the objective is to assess a relationship between an environmental contaminant and a disease. The larger the value of relative risk, the more convincing the evidence that an etiological relationship exists between exposure and the disease. Another measure of disease occurrence is the standardized mortality ratio, a measure of risk relative to that of another population called the standard or reference population. The cross-sectional study evaluates the prevalence of a disease or illness in a population.
Epidemiology provides estimates of the concentration–response relation for environmental and occupational toxicants in the species of interest, in or close to the dose range of interest. As such, when available, they provide the primary source for risk assessments. Further information can be acquired by using modern biostatistical techniques to assess the shape of the dose response relation, examine effect modification, and assure control for confounding. These approaches are particularly effective if they are done in the context of a meta-analysis or hierarchical model. This is illustrated with examples from the air pollution literature.
The notion of hormesis has undergone numerous modifications in the course of the 20th century. Because of its unfortunate association with homeopathy, hormesis did not gain acceptance among biomedical professionals. The lack of a plausible mechanism for its occurrence may have contributed much to the rejection of this concept. This treatise outlines the conceptual struggle for an understanding of the widespread occurrence of low dose effects that appear to be opposite to those caused by high doses as also seen in hormesis. An incomplete conceptualization of time as a fundamental variable of effects (in addition to dose) is identified as one of the major reasons why hormetic responses were not observed more frequently than was reported by Calabrese and Baldwin.7 The definition of hormesis as an (over)compensation response to an inhibitory signal lacks a designation for (over)compensation responses to stimulatory signals in the other direction. Hormoligosis, which was coined by Luckey for all low-dose stimulatory responses of toxins, is suggested as a suitable term for generalizing the latter types of effects. Both types of effects are recognized as originating in a homeostatic overcompensation response that optimizes the ability of an organism to meet challenges beyond the limits of normal (unexercised) adaptation.
Numerous epidemiology studies have evaluated the association between health outcomes in humans and pyrethroid exposure. The purpose of this review was to identify and evaluate the quality of pyrethroid-related epidemiology studies that addressed chronic health effects, and compare findings with animal toxicology studies. We evaluated the quality of 61 studies published between 2000 and 2016 by using elements of outcome, exposure metric, exposure level, and study design. None of the 61 publications demonstrated strong quality for all elements. A few of the outcome measures were strong, particularly those relying upon medical diagnoses. Most of the pyrethroid epidemiology studies used a poor exposure metric, relying upon a single sample of pyrethroid urinary metabolites, which is subject to misclassification of past exposures. In addition, many studies were a cross-sectional design, preventing an evaluation of the temporality of the exposure-disease association.
Ecotoxicology is a multidisciplinary research area in which biologists, chemists, geologists, statisticians, and computer modelers study the toxic effects of environmental agents on biological populations, communities, and ecosystems. Environmental toxicology, a related field, investigates the effects of toxic agents on individual organisms, organs, tissues, cell types, organelles, and biochemical reactions. The Journal of Environmental Science and Health, Part C (JESH-C) aims to publish outstanding scientific review articles and original research reports presenting important and timely subjects in the fields of ecotoxicology and environmental toxicology.
Articles providing novel and relevant mechanistic insights related to the toxicity of natural and manmade materials present in the environment are of special interest to JESH-C and its readers. Deeper mechanistic understandings of how toxic agents affect biological systems adversely may contribute to the development of better methods for control or remediation and improved biomarkers for exposure (Figure 1). In 2016, JESH-C published a review by Liyanage et al. describing the toxicology of freshwater cyanobacteria. The authors found an association between chronic kidney disease of unknown etiology in humans and the presence of harmful cyanobacteria in drinking water which, along with other types of data, utilized the detection of cyanotoxin biosynthesis genes as biomarkers for the presence of harmful algal species.
Figure 1. Mechanistic ecotoxicology and environmental toxicology.