Analysis of pesticide runoff from mid-Texas estuaries and risk assessment implications for marine phytoplankton

During 1993, estuarine surface water samples were collected from the mid-Te xas coast (Corpus Christi to Port Lavaca, TX). Agricultural watershed areas as well as tidal creeks immediately downstream were chosen as sampling sit es along with adjoining bay sampling stations. Collections were made throug hout the growing season (February to October 1993) before and after periods of significant (> 1.25 cm) rainfall. All samples were initially screened f or the presence of pesticides using enzyme-linked immunosorbent assay (ELIS A) test kits (EnviroGard (TM)) for triazine herbicides and carbamate insect icides. All samples were extracted and then analyzed using gas chromatograp hy (GC) for quantification of atrazine. Only samples testing positive for c arbamate insecticides via ELISA were further extracted for GC analysis to q uantify aldicarb and carbofuran. Additionally, laboratory toxicity tests us ing phytoplankton were examined from published, peer-reviewed literature an d compared with the atrazine field levels found in Texas. Results of ELISA screening indicated the presence of triazine herbicides in nearly all sampl es (>93%). GC analysis further confirmed the presence of atrazine concentra tions ranging from <0.01-62.5 <mu>g/L. Screening tests also found detectabl e levels of carbamate insecticides (aldicarb and carbofuran) that were also confirmed and quantified by CC. Comparison of measured concentrations of a trazine compared with published toxicity tests results indicated that there was a potential environmental risk for marine/estuarine phytoplankton in s urface waters of Texas estuaries, particularly when the chronic nature of a trazine exposure is considered.