Doug’s post on July 23 provided an excellent summary of Ecology’s webinar outlining its revision process for water quality standards (WQSs). Integral would like to point out a few more details of interest in Ecology’s approach.
Ecology indicated that it will continue to use bioconcentration factors (BCFs), which estimate concentrations in fish tissue based on concentrations in the water column and so are reasonable predictors for soluble chemicals. But BCFs do not accurately estimate uptake for less-soluble chemicals that may result from a combination of exposures to water, sediment, and the food chain. EPA began recommending the use of bioaccumulation factors (BAFs) in 2000 in its Methodology for Deriving Ambient Water Quality Criteria for Protection of Human Health and has incorporated them into its recently proposed water quality criteria (WQC) for human health. BAFs more accurately reflect uptake for less-soluble chemicals that partition into sediment and the food chain. Integral recommends that Ecology use BAFs to produce more scientifically defensible WQSs; using BAFs and fish consumption rates specific to different trophic levels, which we have suggested previously, would provide the most accurate representation of human exposure through fish consumption.
Doug also noted Governor Inslee’s “no backsliding” policy, i.e., if the updates to toxicity criteria, exposure assumptions, and target risks produce criteria that are less stringent than the current values based on the National Toxics Rule (NTR), then the current values will be retained. For chemicals that may cause cancer, using a higher target cancer risk of 1×10-5 could produce less-stringent WQSs despite a higher fish consumption rate, and the governor does not want to move toward a lower level of environmental protection than was formerly in place.
However, this issue does not apply to chemicals with WQSs based on non-cancer effects. The noncancer toxicity data for some chemicals have been updated since the NTR values were calculated; their toxicities have been shown to be lower than previously understood. These decreases in toxicity produce less-stringent WQSs. Maintaining current WQSs for these chemicals may appear to be environmentally friendly, but it ignores the most current toxicological data and should be discouraged. Non-carcinogens for which Ecology’s revised calculations produce higher WQSs in freshwater include 2,4-dinitrophenol, three forms of endosulfan, antimony, and cyanide. In particular, the updated WQS of 9.7 µg/L for endosulfan is much higher than the NTR value of 0.93 µg/L; despite the fact that current science tells us that a higher concentration is sufficiently protective, Ecology proposes to retain the outdated value. Integral recommends that Ecology strive to use the best science available for setting WQSs.
Finally, Ecology noted that the WQSs will be applied to permitted water discharges as total chemical concentrations measured in the water column, rather than dissolved concentrations. However, it is the chemical concentrations present in the dissolved phase that are available to be taken up into aquatic biota. For chemicals that are released into freshwaters and for which the drinking water pathway is the primary exposure route, evaluating compliance based on total concentrations is reasonable because the water could be used as a source of drinking water without filtering. When measuring compliance for these same chemicals released to marine and estuarine waters, however, an evaluation based on dissolved-phase concentrations would be more appropriate.