An Assessment of the Application Factor Used to Derive the Saltwater Acute Ambient Water Quality Copper Criterion

Abstract

The basis for all US Environmental Protection Agency (USEPA) acute ambient water quality criteria is the chemical specific final acute value (FAV; an estimate of the concentration of the chemical corresponding to a cumulative probability of 0.05 of acute toxicity values for all genera with which acceptable acute tests have been conducted). The acute criterion for all chemicals is equal to the chemical's FAV divided by an application factor of 2. The intention of dividing the FAV by a factor of 2 is to convert the acute toxicity value to an incipient acute toxicity value, resulting in an acute criterion concentration that will protect against toxic effects to aquatic organisms. In the case of copper (Cu) in saltwater, the FAV is reduced from the normal 0.05 probability to equal to the genus mean acute value (GMAV; the geometric mean of copper effect concentration 50% [EC50] values) of the economically important marine bivalves of the genus Mytilus. Analyses to determine an application factor specific to Mytilus and copper were performed to assess the adequacy of the application factor of 2. An estimate of a dissolved copper application factor that is specific to and protective of Mytilus was determined using the results of sixty-four 48-h embryo survival and shell development copper toxicity tests of natural water samples collected from sites around the United States. A variety of point-estimate effects concentrations (EC1, EC5, EC10, EC20, and chronic values [ChV]) and statistical toxic-effect endpoints (no observed effect concentration [NOEC] and lowest observed effect concentration [LOEC]) were derived from the test results and compared. The most similar toxic effect endpoint estimates were EC1 approximately equal to NOEC, EC10 approximately equal to ChV, and EC20 approximately equal to LOEC. Probabilistic methods were used to determine a specific application factor with a high probability of providing protection. This analysis suggests that an application factor of 1.5 (rather than 2) is adequate to provide a high degree of protection against acute effects of dissolved copper to Mytilus. In context, this translates to an acute saltwater dissolved copper criterion of 6.4 microg Cu/L compared to the current acute criterion of 4.8 microg Cu/L.

Acute and chronic cadmium toxicity to a saltwater cladoceran Moina monogolica Daday and its relative importance

“…The maximum-acceptabletoxicant concentration (MATC) or the ''chronic values'' (ChVs) defined by Stephan et al (1985), was estimated as the geometric means of the LOEC and NOEC values. Although NOEC, LOEC, MATC (ChVs) in this study could not be obtained through way of hypothesis testing, some researchers indicated that the most similar toxic effect endpoint estimates were EC1 & NOEC, EC10 & ChV, and EC20 & LOEC (Arnold and Jeffrey 2008). The NOEC (EC1), MATC (EC10) and LOEC (EC20) through point estimates were calculated as 3.01, 1.78, and 1.11 lg Cd/l, respectively, based on R 0 = 53.89 -23.32 Log (Measured Cd) (R 2 = 0.96, P \ 0.01) of regression equation in this study, because the population growth rate has been proposed as a more relevant measurement of toxicant effects than traditional measures of mortality or reproduction in chemical risk assessment (Barata et al 2002a) and net reproductive rate was considered as the most sensitive end point of metal toxicity to M. monogolica .…”