RP8 Ecotoxicology of Agrochemicals and Pharmaceuticals
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(MCD-1117-565133) Impacts of row crop agriculture on sexual development of anurans.

McDaniel, T.¹, Martin, P.¹, Marvin, C,², McMaster, M.², Sherry, J.², ¹ Canadian Wildlife Service, Environment Canada, Burlington, Ontario, Canada² National Water Research Institute, Environment Canada, Burlington, Ontario, Canada

ABSTRACT- Intensive row crop agriculture featuring corn and soybean production, is predominant in southwestern Ontario where the two crops account for over 50% of the total acreage of crops grown. This form of agriculture relies heavily on pesticide and nutrient inputs for continued success under conventional systems. The corn herbicides atrazine and metolachlor, are two of the most heavily applied pesticides in Ontario and are routinely detected in tributaries draining agricultural watersheds. Field and laboratory studies have indicated exposure to atrazine may disrupt normal sexual development in male anurans, causing reductions in testosterone levels, laryngeal muscle diameter, and abnormal testes development. In addition, male cane toads exposed to field levels of atrazine expressed levels of vitellogenin equivalent to those found in female toads. Pesticide levels and water quality data were collected from 33 farm ponds and agricultural drains in southwestern Ontario, two agricultural reference sites as well as four non-agricultural reference sites in August and September, 2003 and monthly from April through August in 2004. Atrazine and metolachlor were detectable in most samples, exceeding 1 ug/L at some sites. Blood samples were obtained from leopard and green frogs for analysis of sex hormones, and vitellogenin. Gonads were excised for histomorphological assessment. Analysis of frogs from late summer 2003, revealed that circulating testosterone levels were negatively correlated with atrazine concentrations in pond water in juvenile male leopard frogs (r = 0.74; p = 0.014) and adult female leopard frogs (r = 0.59; p < 0.008). No relationship was found between sex steroid levels in frog plasma and concentrations of atrazine and metolachlor in the water in 2004, contrary to results from 2003. This may be due to lower concentrations of atrazine and metolachlor in 2004. Agricultural sites, particularly those in Chatham exhibited a high percentage of males with ova-testes (45%), as compared to control sites (10%).

Key words: pesticides, anurans, intersex