R6 PM Bioavailability
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 324-326

(LAT-1117-824132) Calculation of a Water-Effects Ratio for Aluminum in Solutions of Different pH.

Latimer, H¹, Bearr, J¹, Bowersox, M¹, Diamond, J¹, ¹ Tetra Tech, Inc., Owings Mills, Maryland, USA

ABSTRACT- An acute Water-Effect Ratio (WER) study was completed for aluminum in effluent from a drinking water treatment plant in western Maryland. The study approach used was modeled on EPAs 2001-streamlined copper WER procedure. Two paired sets of acute tests were conducted using Ceriodaphnia dubia and Pimephales promelas (fathead minnow). Tests were conducted in site water (pH 7.5 and hardness 80 ppm) and laboratory water (pH 6.5 and hardness 10 ppm). The laboratory water was selected to mimic that used in the studies upon which EPAs 1988 chronic aluminum criterion (0.087 ppm) is based. These tests resulted in a mean final WER of 2.73 for C. dubia and 6.87 for fathead minnow. The larger WER generated by the less sensitive species (fathead minnow) is contrary to EPAs 1994 WER guidance which suggested use of the most sensitive species would yield the highest WER value. Based on an extensive review of the literature conducted in conjunction with this study, we expected that the sensitivity of fish to aluminum would increase more rapidly than that of C. dubia in response to a change in pH. As expected, the difference in pH between the effluent and the synthetic laboratory water resulted in a greater difference in aluminum toxicity to fish than to C. dubia. Although hardness is also thought to mediate aluminum toxicity, the literature is less clear on the effects of hardness on aluminum toxicity while substantial evidence suggests important pH-related effects. Further testing will be necessary to explore the effects of hardness on aluminum toxicity. These results indicate that the abbreviated testing scheme developed for calculation of copper WERs (requires only two sets of paired tests) is appropriate for use with aluminum, however both a fish and invertebrate test species should be used for aluminum WER calculation.

Key words: aluminum, criteria, water-effect ratio, pH