IP01 Ecotoxicity of Pharmaceuticals
B113 & B114
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(IP010) Responses of a freshwater food web to whole-lake additions of a potent estrogen.

Kidd, K.1, 2, Paterson, M.1, Salki, A.1, Findlay, D.1, Blanchfield, P.1, Mills, K.1, 1 Freshwater Institute, Winnipeg, MB, Canada2 University of New Brunswick, Saint John, NB, Canada

ABSTRACT- A whole-lake study was conducted from 1999-2004 at the Experimental Lakes Area in northwestern Ontario to determine whether the potent synthetic estrogen -ethynylestradiol (EE2) affects freshwater food webs. EE2 was added continuously to Lake 260 in each of the summers of 2001-2003 to maintain surface water concentrations between 5 and 6 ng.L-1. Water chemistry and microbial, algal, and zooplankton populations were sampled in this lake bi-weekly during the two years prior to dosing and the three years of EE2 additions, and compared to reference lake samples collected over the same time period. In addition, large and small fish species were monitored for population-level effects in the spring and fall of each year in the EE2 amended and reference lakes. Nutrient concentrations were similar across all years of the study. Microbial abundances ranged from 0.04 to 0.3 mg.L-1 in the study lake, and were similar before and after the additions of the estrogen. The algal biomass in Lake 260 was lowest in 2003 at 465 mg.m-3 compared to 600-900 mg.m-3 in previous years, and this decrease could be related to increased grazing due to changes in the food web structure. Mean annual zooplankton abundances in the study lake were similar from 1999-2002 and ranged between 25 to 40 individuals.L-1; in 2003 zooplankton abundance was 2 to 3 fold higher when compared to data from the previous years. This change in the plankton is likely due to the concurrent decline in the planktivores in this lake. In both 2002 and 2003, reproductive failures occurred for one of the dominant minnow species, the fathead minnow, and the smaller size classes of this species were not present in the fall catches. Results from this study indicate that a potent estrogen can have direct effects on aquatic populations as well as indirect effects through a trophic cascade.

Key words: estrogen, food web, populations

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