Dean Wilson, Water Quality Scientist King County DNRP Diazinon and Carbaryl Concentrations in Thornton Creek and Comparison to Retail Sales

EPA announces diazinon phaseout (Dec 5, 2000) Retail sales of active ingredients at Lowe’s and Home Depot stores in King County * * Source: CCI Triad, Reports for LHWMP (King County)

DIAZINON & CARBARYL Insecticide Organophosphate General garden and turf use Not allowed on golf courses Sales for urban uses ended Jan 1, 2005 Highly toxic to fish Insecticide Carbamate General garden use, slug/bug bait, turf Promoted as “alternative” to diazinon EPA may limit turf use Moderately toxic to fish DIAZINONCARBARYL

Urban Runoff

Mobility Comparison DIAZINON Soil half-life:40 days Koc:1000 SWMI:*0.26 CARBARYL Soil half-life:10 days Koc:300 SWMI:0.37 SWMI MODEL* PREDICTION Assume all diazinon replaced by carbaryl Assume products used at maximum rates allowed on label Result: carbaryl in streams would be 3-4 times previous diazinon levels. *Chen W, et al Envir Toxicol Chem 21: C p(x) = R label f c  SWMI) 

Thornton Creek Watershed Primarily urban 12.1 square miles 75,400 people, 33,362 households 38% single-family dwellings 51% residential 23% roads and shoulders 8% commercial (includes Northgate Mall) 4% parks, 4% schools

Measured Diazinon (µg/l) in Thornton Creek Data from U.S. Geological Survey EPA standard=

Measured Carbaryl (µg/l) in Thornton Creek Canadian guideline=0.2 Data from U.S. Geological Survey

Summary Diazinon concentrations have declined (p=.002, median decr. 3.2) along with sales Carbaryl concentrations have increased (p<0.001) along with sales More sales = more use = more pollution Other issues

Toxic Tradeoff: Two snapshots of insecticide mixture in Thornton Creek + = Canadian chronic guideline

Epilogue: * DIAZINONCARBARYL *NOTE: the 2004 data have not yet been officially released by USGS and values may change.

The next chapter? Source: CCI Triad (data for King County)

Closing Thoughts Diazinon phaseout has reduced concentrations in Thornton Creek Consumers switched from diazinon to carbaryl in 2002, leading to higher carbaryl concentrations in Thornton Creek Ortho began phasing out carbaryl lawn formulations after 2002 in favor of pyrethroids Thornton Creek carbaryl concentrations have dropped somewhat in 2003 and 2004 relative to peak in Retail sales combined with mobility models could help predict stream pesticide concentrations and identify future problems.