Atrazine and Metolachlor Contamination in Surface and Ground Water in the Zomba/Bvumbwe Region in Malawi

Abstract

A snapshot survey was conducted to assess ground and surface water contamination by atrazine and metolachlor in the Zomba/Bvumbwe region. Ground and surface water samples were collected and their atrazine and metolachlor were extracted using ethyl acetate. The extracts were cleaned up using florisil, concentrated on a rotary evaporator and detected using thin layer chromatography. No herbicide residue was detected in the groundwater samples. In surface water samples atrazine was detected in 38 % and metolachlor was detected in 15 % of the samples. The concentrations of the herbicides were at their highest soon after the first run off event after herbicide application. The concentrations, however were generally below the World Health Organization's (WHO's) recommended maximum guideline values (2 μg/ml atrazine and 10 μg/ml) metolachlor. Following the first run off event concentrations of herbicides steadily decreased with time, decreasing to zero within eight weeks of herbicide application at 37 % of the water sampling points that had herbicide contamination. Light soaking rains, higher clay content, flat land, longer distance between agricultural land and surface water body (filtering area), lower herbicide application rates and herbicide incorporation seemed to reduce herbicide export to surface water. Based on the study it is recommended that regular monitoring of pesticides in water should be done and that quantification of the pesticides should be done more accurately using a gas or liquid chromatograph with appropriate detectors. It is also recommended to follow good land husbandry practices to reduce export of pesticides to surface water bodies.