Contamination stressors

Schnurr et al. (1996) postulate that these exposures involved elements of contamination stressors in which information about the exposure is the stressor rather than the tangible event. The late disclosure of the dangerous nature of these tests served as an additional stressor for many of the exposed men. Lack of information during the test, leaning to vague or diffuse fear with unknown consequences, could also contribute to the development of PTSD. The contamination stressor led to a future orientation a worry about what problems will develop as a result of the previous exposure. 

Only a small fraction of faecal contaminants contributed to the enviromnent through human and animal faeces reach new hosts to infect them. Many of the defecated microorganisms never reach the soil and/or water bodies, since faecal wastes are submitted to purification (water) and hygienization (solids) processes, which remove a fraction of the pathogens and indicators. An important fraction of those that reach either the soil or water are removed (adsorption to soil particles and suspended solids, followed by sedimentation) and/or inactivated by natural stressors (physical, chemical and biological) in soil and water bodies. 

The virus-associated mass mortalities that took place among marine mammals in the 1980s and 1990s elicited an interest in co-factors that may have contributed to the severity of these events. The deaths of 20,000 harbor and several hundred grey seals in northern Europe in 1988 prompted questions about climate change, algal blooms, environmental pollutants, exotic diseases and other perceived stressors [54], After the identification of a newly described virus, phocine distemper virus (PDV) [55], concern still lingered that immunotoxic environmental contaminants could have facilitated the outbreak. 

Most of our knowledge of the biological effects of petrolemn pollution is based on studying the acute effects of major spills or heavily contaminated sediments. These effects tend to be directly lethal. Acute toxicity has been foimd to be largely related to water solubility, with cmnulative toxicity reflecting the smn of the effects of each individual hydrocarbon. Relatively little is known about the effects of chronic exposures at lower concentrations, especially in the presence of other stressors, such as heavy metals. Effects of chronic inputs from land-based sources on populations, communities, and ecosystem structure and function are also not sufficiently known. 

The Pellston workshop in February 2002, which produced this book, aimed to develop guidance and increased consensus on the use of uncertainty analysis methods in ecological risk assessment. The workshop focused on pesticides, and used case studies on pesticides, because of the urgent need created by the rapid move to using probabilistic methods in pesticide risk assessment. However, it was anticipated that the conclusions would also be highly relevant to other stressors, especially other contaminants. 

Allows for (1) interactions between contaminants in complex sediment mixtures (additivity, antagonism, synergism) (2) actions of unmeasured toxic chemicals (3) actions of other stressors (physical, biological). 

Though developed for use with chemical contaminants, can be applied to other stressors (physical, biological). 

Hazard assessment Process that evaluates the type and magnitude of adverse effect(s) caused by a stressor (such as chemical contamination). Volume 2(8,10). 

An important characteristic of biomarkers is that they indicate that a contaminant (or contaminants) is (are) present in the environment, that it is biologically available, and that it has reached a target tissue in sufficient quantity and duration as to elicit the observed response (Melancon 2003). In addition, because most organisms are exposed to multiple stressors over time, biomarkers can reflect an integrated exposure of cumulative, synergistic, or antagonistic effects (Adams and Rowland 2003). 

If, through a proper landscape analysis, a realistic combination of multiple stressors is identified, food-web models may be used to predict and extrapolate their ecological effects to relevant ecosystems of the landscape unit of concern. An overview of models that can be used for the integrated assessment of eutrophication and organic contaminants in aquatic ecosystems is provided by Koelmans et al. (2001). Examples of aquatic food-web models that can be used or adapted to predict effects of multiple stressors are IFEM (Bartell et al. 1988), AQUATOX (Park 1999), and C-COSM (Traas 2004). 

Cumulative risk assessments evaluate the health risk for aggregate exposures accumulated over time and for multiple contaminants or stressors. In some contexts (e.g. USEPA pesticide risk assessments), cumulative refers specifically to combined exposures to chemicals that share a common mechanism of toxicity (see http // www.epa.gov/oppsrrdl/cumulative/). Populations may be defined by their location relative to sources, their activities and customs, and their susceptibility to exposures. In this context, populations can include different ethnic groups, different communities, or different age groups. Cumulative risk is a very important concept in understanding environmental health risks to children in different settings, particularly in underdeveloped countries where children may be facing multiple stressors. 

Cumulative risk is the combined risk resulting from exposures that accumulate over time, pathways, sources, or routes for a number of agents or stressors. This concept of cumulative risk addresses the fact that individuals are not usually exposed to a single environmental contaminant by means of a single exposure pathway. Multiple contaminants are released from sources as chemical mixtures. Environmental fate and transformation processes affect the nature, pathways, and extent of human exposure. Exposures by different pathways may result in differential absorption, metabolism, and toxic response, even for the same chemical. Cumulative risks are... 

---