RP10 Aquatic Ecotoxicology
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(RAL-1117-844847) Species sensitivity distribution of aquatic biota exposed to soybean rust fungicides.

Ralston-Hooper, K¹, Ochoa-Acuna, H^{2, 3}, Hahn, L⁴, Shaner, G⁵, Sepulveda, M^{1, 3}, ¹ Department of Forestry and Natural Resources, Purdue University² Department of Veterinary Pathobiology, Purdue University³ Department of Civil Engineering, Purdue University⁴ Office of Indiana State Chemist⁵ Department of Botany and Plant Pathology, Purdue University

ABSTRACT- Asian soybean rust Phakopsora pachyrhizi is a highly contagious, fungal crop disease recently detected in several US states. The introduction of this pest has prompted the EPA to approve emergency exceptions for several fungicides that have not yet been registered for use in the US. To date, 14 active ingredients (azoxystrobin, chlorothalonil, cyproconazole, famoxadone, flusilazole, flutriafol, metconazole, myclobutanil, propiconazole, prothioconazole, pyraclostrobin, tebuconazole, tetraconazole, and trifloxystrobin) have been approved for use against soybean rust, of which only three (chlorothalonil, azoxystrobin, and pyraclostrobin) have been granted full registration. Given that the vast majority of fungicides under evaluation lack data on chronic exposure for invertebrates and alga, two toxicity tests were conducted for all active ingredients: the chronic 7-day Ceriodaphnia dubia survival and reproduction test and the chronic 4-day green alga Selenastrum capricornutum growth test. Toxicity tests were also performed using Diporeia spp. and Hyallela azteca. Risks were evaluated through the development of species sensitivity distributions of lowest effects (LOEC), no observable effects (NOEC), and median effects (EC50) concentrations using published data, values extrapolated using computational toxicology approaches, and results of these toxicity tests. Aquatic organisms encompass a wide range of physiological and life history characteristics, and therefore their sensitivity to a particular chemical can vary considerably. Species sensitivity distributions provide a statistical mechanism for describing such interspecific variation.

Key words: soybean rust, toxicity, ceriodaphnia dubia, fungicide