In November 2002, EPA revised over half of the recommended WQC for the 158 chemicals. In the December 27, 2002 Federal Register, EPA issued a notice on revised WQC for 15 additional compounds, including cyanide, toluene and vinyl chloride EPA's recommended WQC provide guidance for establishing WQC under the Clean Water Act to protect human health and aquatic life. The WQC are typically used for surface water bodies, such as rivers and lakes.
With these latest revisions, EPA modified the WQC for 98 compounds. Most of these revisions are to protect human health. Human health criteria are based on the assumption that somebody could eat fish and drink water from a water body, or only eat fish from a water body. The revisions incorporate new toxicity information on compounds and other changes in the calculation method.
For many of the chemicals, including polychlorinated dioxins (PCBs) and dioxins, the water quality criteria are now lower (more stringent) than before. These changes have the strong potential to require more aggressive remedial measures at hazardous waste sites as well as more rigorous controls for wastewater dischargers.
For others, such as methylmercury, EPA uses a new type of WQC which is likely to change how water body compliance is assessed. Methylmercury's criterion is now expressed as a fish tissue value of 0.3 mg/kg, rather than as a water concentration; this reflects scientific consensus that consumption of fish and shellfish is the main human route of exposure to methylmercury. EPA plans to develop guidance to assist states and tribes with implementing the methylmercury criterion in WQS. The new WQC is likely to require fish-tissue sampling and more direct assessment of human health risk associated with consumption of fish.