Risk-based action levels

A risk-based action level obtained from an ecological risk assessment is 1 microgram per kilogram (pig/kg) TEQ. The action level (discharge permit limitation) for each of the contaminants of concern is 1 microgram per liter (pg/1). 

Risk-based action levels are calculated concentration values that may be lower than the current detection capabilities of analytical methods. In such cases, a PBMS, specifically developed to meet an unusually low detection limit, may be a solution. However, some calculated risk-based action levels cannot be attained even with the most advanced analytical techniques. 

Tier 1 uses conservative, health-protective levels to compare to site-specific data to eliminate those sites not requiring remediation beyond monitoring (the obvious monitoring-only sites). The Tier 1 risk-based screening levels (RBSLs) typically incorporate very conservative or worst-case exposure assumptions. However, many sites with concentrations exceeding the RBSLs do not necessarily pose a threat to human health. Therefore, exceeding values of RBSLs by themselves do not indicate that remedial action should be actively undertaken to protect human health and the environment. 

Each risk-based remedial action objective for an exposure pathway will typically include numeric remedial action levels for each contaminant. Remedial action levels may also be developed for non-risk remedial action objectives such as resource protection standards. The non-risk remedial action levels may include thickness or mobility criteria for non-aqueous phase liquids (NAPL). 

A remedial action is required if environmental media contain contaminants at concentrations above the risk-based or non-risk remedial action levels. If all contaminant concentrations are below the remedial action levels, then no further action is required. 

An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure. MRLs are based on noncancer health effects only and are not based on a consideration of cancer effects. These substance-specific estimates, which are intended to serve as screening levels, are used by ATSDR health assessors to identify contaminants and potential health effects that may be of concern at hazardous waste sites. It is important to note that MRLs are not intended to define clean-up or action levels. 

HBM values are derived from toxicologic and human studies and are health based (Jakubowski and Trzcinka-Ochocka 2005). Two types of HBM values exist HBM I, the concentration of an environmental toxin in human biological material below which there is no risk of adverse health effects and HBM II, the concentration above which there is an increased risk of adverse health effects in susceptible individuals in the general population (Jakubowski and Trzcinka-Ochocka 2005). An HBM I value serves as an alert level, and an HBM II value is an action level at which immediate efforts should be made to reduce exposure and further clinical examination should follow (Ewers et al. 1999). HBM values and reference values have been derived for a number of chemicals, including lead, cadmium, mercury, pentachlorophenol (PCP), and arsenic. 

For food safety purposes the overriding aim is that food contamination should be reduced to the lowest practicable level, bearing in mind the potential costs and benefits involved. Since it is difficult to establish cause and effect relationships following long-term (chronic) exposure at low concentrations, it may be necessary to base action on prudence rather than on proven harm to health. However, if this approach is to maintain the confidence of both consumers and producers of food, a rational evaluation of all relevant information is required so that the balance between the risks and benefits of veterinary drugs can be assessed. Information on the incidence of potentially harmful drug residues is fundamental to this cost-benefit analysis so too is the consumption of the commodities involved (particularly for susceptible consumers or those consumers who eat more). Account must also be taken of the potential fall in food production if a drug is controlled or prohibited, and also the animal health and welfare implications that may result from the restriction of an animal medicine for which there may be no effective alternative. 

Action level for dioxin and dioxin-like compounds in soil. Action levels are concentrations of chemicals at which consideration of action to interdict exposure occurs 1 ppb TCDD in residential soil was identified by Kimbrough et al. (1984) as a "level of concern" and recommended as "a reasonable level to begin consideration of action to limit exposure." The conclusions of Kimbrough et al. (1984) were derived in part from an evaluation of the carcinogenic potential of TCDD, based on a 2-year oral chronic toxicity and oncogenicity study in rats (Kociba et al. 1978). With the advancement of knowledge about dioxin-like chemicals and their assumed common mechanism of toxicity, the TEQs were introduced into the risk assessment process. Since then, 1 ppb of total dioxins (expressed as TEQs) in soil has been used as an action level by ATSDR. 

---