Current-use insecticides, phosphates and suspended solids in the Lourens River, Western Cape, during the first rainfall event of the wet season

Abstract

Pesticide contamination resulting from agricultural runoff depends on the time period between application and rainfall. In Western Cape orchard areas, the last pesticide application of the growing season in summer takes place at the end of February. Pesticides, total phosphates and total suspended solids (TSS) were measured in the Lourens River at the beginning of April 1999 prior to the first rainfall of the rainy season and in the middle of April during high discharge following the first rainfall of 9.6 mm/d. Pre-runoff samples indicated only contamination with total endosulfan (α, β, sulphate) at levels up to 0.06 µg/l. Runoff during the first rainfall event resulted in an increase in the levels of endosulfan, chlorpyrifos and azinphos-methyl, to 0.16, <0.01 and 0.38 µg/l, respectively, in water samples and 245, 344, and 244 µg/kg in suspended sediments. In terms of chemical load the single rainfall event caused a loss of 15.1 g/h endosulfan, 1.8 g/h chlorpyrifos and 20.5 g/h azinphos-methyl. The second rainfall event caused no measurable increase in pesticide levels, although the amount of rain was even higher (14.4 mm/d). Levels of both total phosphate and TSS were also increased during the first runoff event. Transient contamination levels exceeded the target water quality range proposed by the South African Department of Water Affairs and Forestry (DWAF). The Lourens River site downstream of the farming area is identified as a site where potentially toxic conditions might arise.

Insecticides and a fungicide affect multiple coral life stages

“…Levels of pesticides in suspended sediments and in solution can increase dramatically following the first rainfall of the wet season. For example, chlorpyrifos concentrations in suspended sediment rose from below detection limits to 344 µg l -1 in the Lourens River, following the first heavy rains of the South African wet season (Schultz et al 2001).…”

Influence of irrigation on the occurrence of organic and inorganic pollutants in soil, water and sediments of a Spanish agrarian basin (Lerma)

“…Such contamination does not represent a danger exclusively to the agrarian area, as it can be transported to other zones, especially during heavy rain events (Carter, 2000;Schulz et al, 2001). In general, the surface waters of the Ebro basin present a low level of pesticide contamination in accordance to the vulnerability limits imposed by European Union legislation.…”

“…Although atrazine, metolachlor, terbuthylazine and chlorpyrifos are present in the principal pesticides applied in the basin, they were not detected in the soil. It is possible that the absence of such substances in the samples was due to leaching to deeper layers of soil or runoffs, circumstances normally caused by precipitation events or irrigation after the application of pesticides (Carter, 2000;Schulz et al, 2001). The analyzed PCBs were not detected in the samples either, as they normally originate from industrial areas (Mañosa et al, 2001).…”

Uptake and distribution of copper in the freshwater crab Potamonautes perlatus (Crustacea) in the Eerste River, South Africa

“…Rivers are very vulnerable since waste in effluents from point sources and other contaminants from industries, homes and farms reach them either directly through spraydrift or runoff (Robinson & Avenant-Oldewage 1997;Schulz et al 2001) or through groundwater seepage. Heavy metals can enter the food chain through air, water, soil and organisms and are derived from industrial effluents, agricultural runoff, mining and mineral processing, stormwater runoff, natural erosion of bedrock, and atmospheric transport.…”