Seasonal variation of carbaryl and cypermethrin in soils, ground water and surface water in a cotton growing area of Lisungwi in Neno district, Malawi

Abstract

Pesticides play a vital role in crop production in Malawi through the reduction of insects, weeds, plant diseases and other pests. However pesticides contaminate the environment including catchment areas which in turn may affect both human health and aquatic life. This study was conducted to assess the presence of pesticides, Carbaryl and Cypermethrin in water and soil from Lisungwi area, Neno district, southern Malawi. The area from which samples were collected is dominated by high pesticide usage especially in cotton fields. Carbaryl (a carbamate) and Cypermethrin (a pyrethroid) are the mostly used pesticides in cotton production hence being the main focus of the study. In this study, soils, surface water and ground water samples were collected in both the rainy season and dry season to assess the presence of Carbaryl and Cypermethrin. This was in addition to the assessment of selected physico-chemical parameters which included nitrates, phosphates, pH, temperature, total dissolved solids and electrical conductivity using standard methods especially from American Public Health Association (APHA), and Association of Official Analytical Chemists (AOAC). Carbaryl and Cypermethrin were extracted using organic solvents, and quantified using HPLC-DAD and UV spectrophotometer, respectively. There were no guideline values for Carbaryl from World Health Organization (WHO) and Malawi Bureau of Standards (MBS). Furthermore, no guideline value for Cypermethrin was highlighted by MBS. The results showed that all physico-chemical parameters were within accepted limits set by World Health Organization (WHO) and Malawi Bureau of Standards (MBS) except for phosphates and electrical conductivity. The results further confirmed the presence of both Carbaryl and Cypermethrin residues in water (both surface and groundwater) and soil samples. The average concentration of Carbaryl for surface water in rainy season was 0.14 ± 0.08 ppm, and 0.26 ± 0.12 ppm in groundwater. The average concentration of Carbaryl residue in the surface water was 0.05 ± 0.07 ppm and 0.01 ± 0.01 ppm in ground water vii during the dry season. There were no significant differences in Carbaryl residues in the surface water and ground water in rainy season and dry season (p > 0.05). Furthermore, average Carbaryl residue for soil in the rainy season was 1.23 ± 0.48 ppm and 1.19 ± 0.04 ppm in the dry season. Carbaryl residues in soil was statistically significant in the rainy season than dry season (p < 0.05). There was no significant difference (p > 0.05) in the concentration for the Cypermethrin residue in the rainy season in the surface water (Mean = 11.16 ± 3.3) as compared to ground water (Mean = 7.27 ± 2.89). Cypermethrin concentration in surface water for the dry season was not statistically significant (p > 0.05) (Mean = 3.95 ± 5.53) compared to ground water (Mean = 7.23 ± 4.95). The average concentration of Cypermethrin residue in soil samples for the rainy season was 0.29 ± 1.02 ppm and in the dry season it was 0.04 ± 0.00 ppm. Cypermethrin in soil was not statistically significant (p > 0.05) in the rainy season as compared to the dry season. Carbaryl residues in water and soil were above Australian guideline (0.003 mg/L) and Canadian guideline (0.09 mg/L) for drinking water in both seasons. Cypermethrin residues in water were above United States Maximum Residual Limit (US MRL), (0.05 μg/L), WHO limit (0.05 μg/L) in both seasons. The soil samples exceeded the US MRL guideline value (0.05 mg/Kg) in the rainy season only. The water and soil in the study area get contaminated easily with the pesticides applied in the cotton fields. Among others, it is recommended that there is a need for the routine monitoring of pesticide residues in the study area so as to reduce and control environmental pollution.