Upper Ballona Creek Toxicity from Synthetic Pyrethroids: A Predictive Model Based on Land Use
Pyrethroid pesticide mass loadings in Ballona Creek Watershed were calculated using the Volume-Concentration Model with GIS to explore potential relationships between urban land use and impervious surfaces, and pyrethroid runoff flowing into Upper Ballona Creek. Volume-Concentration Model refers to a series of equations relating storm water runoff volume and storm characteristics, for which PLi = RV x EMCi estimates pollutant loads, where RV is the storm runoff volume and EMC is the average pollutant concentration during a storm event. While EMCs exist for a variety of pollutants and land uses, an EMC for pyrethroids has yet to be calculated. Based upon historical usage of pesticides, and assuming pyrethroid transport and fate are the same as diazinon, a method using 2003 pyrethroid and diazinon data from the California Department of Pesticide Regulation (CDPR) Pesticide Use Database (PUR), calculated pyrethroid EMC from diazinon geometric mean concentration from residential land use. EMC = 0.13 ug/L (0.02 ug/L x Total Reported Pyrethroid Reported Non-Agricultural Use ÷ by Reported Non-Agricultural Diazinon Use). EMCs for anything other than grouped residential and commercial land use were given a 0 μg/L. Rainfall was averaged from the past 10 years data (14.789 in) from the Los Angeles Almanac. Calculations were made per land use category in GIS (each land has its on RC) and then converted to g/L. Weighted overlay analysis and exponential decay were used to show the effects of pyrethroid mass, distance from the creek, and land use. GIS-Volume Concentration Model was calibrated against 2013 and 2014 dry and wet weather sampling data. This model has significant implications for determining mass loadings due to land use influence. GIS modeling offers a cost effective way to use real time data for a small amount of samplings and extrapolate information for a larger watershed area.