Pesticide Residues in Surface Waters of North Carolina Rural and Urban Watersheds: Studies to Determine and Reduce Residues in Drinking Water.

Abstract

The practice of using pesticides on agriculture, commercial landscapes, residential lawns, highway rights-of-way, and recreational areas such as golf courses has resulted in non-point source contamination of surface waters via runoff. Assessment of human health implications of non-point sources within watersheds involved residues of selected pesticides monitored from 1999 to 2001 in surface waters that serve as drinking water sources of five rural and urban watersheds in North Carolina. Approximately 1500 samples from 90 sites were screened with Enzyme-Linked Immunosorbent Assay (ELISA) for atrazine, alachlor, simazine, chlorpyrifos, chlorothalonil, metolachlor, and 2,4-D. The residue concentrations exceeding 1.0 μg/L were extracted with C18 Empore™ Disks and analyzed by gas chromatography/nitrogen phosphorous detection (GC/NPD) for confirmation.

The seven compounds showed similar pesticide concentrations in both rural and urban watersheds. The rural watersheds most often exhibited residues of atrazine, simazine, and 2,4-D while metolachlor and 2,4-D were chiefly found in urban areas. Pesticides intermittently exceeded established maximum contaminant levels (MCL) and led to further monitoring of raw and finished waters of treatment plants within the watersheds. Atrazine, simazine, metolachlor, 2,4-D residues were found in pre- and post-treated water at comparable levels, indicating little change in pesticide concentrations following standard treatment procedures.

Remediation efforts focused on prevention of non-point sources of atrazine in a rural watershed. Atrazine residue levels were lowered as a result of source prevention implementation with the cooperation of municipalities, farming community, and county agricultural extension agents. The prevention measures involved alternatives to atrazine applications and utilizing either less-persistent pesticides or genetically modified seed.

Additional remediation efforts involved the adsorbent ability of powdered activated carbon (PAC) as a treatment method for reducing pesticide residues in drinking water supplies. Studies with PAC combined with water fortified with a pesticide mixture of atrazine, chlorpyrifos, simazine, and metolachlor exhibited declines in residues from 25 to 100% of initial concentrations with 10 mg/L of carbon. Aluminum sulfate (alum) was combined with PAC in studies with atrazine and metolachlor to determine effects of contact time on the adsorption of the pesticide residues. Carbon alone adsorbed 5 to 30% more pesticide residues than carbon and alum combined and alum alone had minimal effects on residues of atrazine and metolachlor.

Further carbon studies simulated treatment plant procedures to determine effective points of PAC addition within the treatment train of a model drinking water treatment plant. A carbon concentration of 20 mg/L was most efficient in reducing pesticides residues and carbon added prior to or after alum resulted in adsorption of atrazine, metolachlor, simazine, and alachlor residues that was more effective than simultaneous addition of the two chemicals.