PM16 Molecular Indicators for Ecological Exposure
Exhibit Hall
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(PM271A) Exposure of salmonids to carbaryl following applications to control burrowing shrimp.

Major, III, W, Grue, C, Cabarrus, J, Grassley, J, Overman, N, Dumbauld, B,

ABSTRACT- Recent efforts to restrict/prohibit the use of carbaryl to control burrowing shrimp (Neotrypaea californiensis and Upogebia pugettensis) have been in part driven by concerns over effects on salmonids documented in laboratory studies, and not actual exposure during operational applications. Data on the actual exposure of salmonids to carbaryl are lacking, threatening the permitting process and control operations. In summer 2003, we studied the use of treated areas by salmonids in an effort to quantify their actual exposure to carbaryl. Use of the water column above oyster beds by salmonids was determined on the first daylight high tide at each of three oyster beds (10-25 ac) preceding two carbaryl spray events (2 and 14 July 2003), and during each of the three subsequent daylight high tides (ca. 6, 30, and 54 h after treatment). Sampling methods included use of a two-boat trawl net and gill nets. The only salmonid captured before and after treatment were juvenile chinook (Oncorhynchus tshawytsha). Juvenile chinook were captured on all sites and all sampling periods. Concentrations of carbaryl before each of the two spray events were < 1 ppb (ND, below detection limits); concentrations after spray ranged from ND to 11.3 ppb. These levels are 2-3 orders of magnitude below levels lethal to chinook (LC50carbaryl = 2,400 ppb, LC501-naphthol = 1,400 ppb [rainbow trout]). Brain AChE assays showed statistically significant levels of inhibition (∼10%) during the first tide post treatment on one spray event with recovery to pre-spray levels of AChE by the second tide post-treatment. Both spray events showed significant increases (∼5-10%) in AChE levels by the third tide post treatment. Our results suggest that juvenile chinook are being exposed to low levels of carbaryl over at least 50 h, but are not exhibiting levels of AChE inhibition associated with mortality or overt behavioral effects.

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