Cumulative exposure defined

Exposures resulting in nonlethal, irreversible effects of dimethylhydrazine were not well defined. For most studies, responses were described in terms of no visible signs of toxicity or lethality. However, Weeks et al. (1963) described nonlethal (but reversible) effects in dogs exposed to 1,1-dimethylhydrazine at varying concentrations. In this study, dogs were exposed to 1,1-dimethylhydrazine at 1,550 ppm or 4,230 ppm for 5 min or 360, 400, or 1,530 ppm for 15 min. The highest cumulative exposures at each of two exposure periods (Ct =352-383 ppm-h) were associated with marked tremors, convulsions and death, while the lower concentration exposures at each of two periods caused behav... 

Cumulative risk assessment The evaluation of the risk of exposure to two or more chemicals. The USEPA defines cumulative exposure under the Food Quality Protection Act to be the evaluation of the risk of exposure to two or more pesticides that work through a common mechanism of action. 

Cumulative exposure is defined as the combined exposure of a target to two or more pesticides (with a common mechanism of action) via all relevant pathways and sources . The US FQPA and the Canadian PCPA mandate the consideration of aggregation of pesticide chemical residues from dietary and residential exposures, and cumulative exposures of pesticide chemical residues with common mechanisms of action. This presents a formidable methodological challenge to exposure assessors. 

Although the data are not sufficient to define the shapes of the dose incidence curves in most instances, a markedly increased risk of cancer has been noted in a number of more heavily exposed populations (Ikble 6.5). In 2-naphthylamine distillers, for example, the latency and incidence of bladder cancer have been observed to vary systematically in relation to the duration of exposure (Figure 6.2). In those with exposures lasting more than five years, the cumulative incidence approached 100 percent (Figures 6.2 6.3). 

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. 

CHARACTERIZING DOSE AND RISK IN A CUMULATIVE ASSESSMENT 277 CASE STUDY 280 Case Study Defining Risk 280 Case Study The Dose-Response Relationship 280 Case Study Using the Margin of Exposure to Characterize the Risk 281 Case Study Benchmark Doses 282 Case Study Margins of Exposure 284... 

---