Cumulative Risk Assessment Framework for Waterborne Contaminants

Abstract

A framework is developed and applied for semi-quantitative estimation of cumulative risk from complex mixtures of compounds in water supplies. The framework places these risks onto the unifying metric of Disability Adjusted Life Years (DALYs), and harmonizes cancer and non-cancer, morbidity and mortality, effects. The framework can be used to: 1) calculate a measure of cumulative risk for a given supply, and compare this measure across supplies or across the same supply with candidate treatments applied; 2) identify those compounds contributing most significantly to cumulative risk, so risk management measures can be applied most effectively; and 3) quantify the influence of different regulatory limits, for specific compounds, on the cumulative risk from drinking water. Results of application to a hypothetical water supply in which all compounds are at their existing Maximum Contaminant Level (MCL) show the cumulative risk for even a complex mixture may be dominated by a few compounds. In this application, that risk was dominated by as few as 10% of the compounds. The analysis also shows that establishing MCLs based on compounds for which there is an oral slope factor, but where no cancer-based limit has yet been established, probably will have little influence on the relative cumulative risk (as measured by Total Weighted DALY) of different water supplies. This arises primarily because the non-cancer-based MCL is usually more restrictive than the one based on cancer for target probabilities of cancer equal to 1E–4 or 1E–5

Prioritizing hazardous pollutants in two Nigerian water supply schemes: a risk-based approach

“…Crawford-Brown and Crawford-Brown 4 and Pennington et al 19 argue that measures of toxicity, such as the reference dose, acceptable daily intake, tolerable daily intake and minimal risk level, were developed for assessing the health risk of individual hazardous substances in a regulatory context, not for comparing hazards. Consequently, CrawfordBrown and Crawford-Brown proposed using the 1% benchmark dose as the metric of toxicity for the noncancerous effects of a substance.…”

“…In assessing the risk to health associated with the presence of a particular metal, we adopted the approach used by Crawford-Brown and Crawford-Brown, 4 who related the risk of each individual health outcome associated with a particular metal to the probability of that health outcome occurring and the severity of the outcome, expressed in DALYs:…”

“…As a summary measure of biologically relevant exposure to a metal in water, we used the chronic daily intake of the metal, in mg per kg per day, by children and adult females and males, as defined in Equation 3, Equation 4 and Equation 5. [13][14][15][16] For the oral ingestion of treated water:…”

“…However, in addition to concentration, the risk-based approach also takes into account parameters such as the level and duration of exposure to contaminants, their toxicity and the severity of the diseases they produce in assessing the need for mitigation. Furthermore, since this approach involves estimating the number of disability-adjusted life years (DALYs), it provides a framework for systematically comparing the disease burden associated with different pollutants, 4 whether microbial, chemical or radiological. 1 In this paper, we used a risk-based approach to identify the pollutants that posed the greatest risk to human health in two Nigerian water supply schemes and which should, therefore, be prioritized for removal.…”

Critical review of methodology and application of risk ranking for prioritisation of food and feed related issues, on the basis of the size of anticipated health impact

“…The proportion and incidence of individuals at risk (toxicity x exposure x population at risk) is estimated and mean individual total DALY values are calculated by summing individual risk (DALYs) for each compound, and for the whole population at risk (Crawford-Brown, 2012;Etchie et al, 2013).…”