Chemical risk is a function of both exposure and hazard, thus either low hazard and/or low exposure implies low risk. In the US EPA New Chemicals Program under TSCA, often little or no toxicology data is submitted with a pre-manufacture notification chemical. Structure-activity relationship strategies can identify analog(s) to characterize the toxicity point of departure (POD) and exposure potential for a chemical. In the absence of such analog data/information, other qualitative strategies are needed to characterize a chemical to ensure that it is not likely to pose an unreasonable risk to health or the environment.<br/>Various strategies are available to characterize risk qualitatively. One strategy is to calculate a “threshold dose producing acceptable risk” based on conservative oral, dermal or inhalation exposure information, in lieu of a POD derived from a toxicology study. A low dose required for hazard would make it unlikely to cause concern and thus the chemical may be deemed not likely to pose an unreasonable risk. Physical-chemistry data (i.e., solubility, log Kow, vapor pressure, molecular weight, etc.) can also be utilized to qualitatively characterize risk and inform safety decisions for all three routes of exposure. Very high log Kow compounds bind so tightly to the stratum corneum layer in the skin that very low dermal absorption or internal doses would likely occur. Thus, the systemic toxicity via the dermal route would not likely pose an unacceptable risk, in the absence of dermal corrosion or sensitization. For drinking water risk, chemicals with extremely low water solubility (i.e., 1 ppb), if characterized based on the estimated daily consumption of water, would require consumption of dozens of liters of water/day to achieve an adverse effect. Thus, calculation of a “threshold water concentration below which risk would be not likely” can be utilized to qualitatively characterize the risk for drinking water consumption. Chemicals in liquid form with very low vapor pressures would tend to pose little opportunity for inhalation exposure, in the absence of spray applications; hence a possible similar risk finding of “not likely”.<br/>This work will highlight several case studies illustrating how these qualitative strategies can be used to assess the risk of chemicals in the absence of a toxicity POD.<br/>

Qualitative assessment of risk strategies within the US EPA New Chemical Programs under the Toxic Substances Control Act (TSCA)

254th National Meeting (2017)

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