Contamination of River Nzoia by Alachlor Metolachlor And Their Degradation Products

Abstract

Pollution of River Nzoia by pesticide has been suspected for sometime because the river drains one of Kenya's largest and richest agricultural basins. Improper agronomic practices have rendered the River Nzoia basin prone to massive soil erosion and pollution of the River Nzoia by agrochemical run-offs. Although 2- chloro-2' ,6' -diethyl-N-methoxymethyl)acetaniline(alachlor) and 2-chloro-N-(2- ethyl-6-methylphenyl)-N-(2-methoxy-1-ethyethyl)acetamide(metolachlor) are widely used herbicides in the river catchment basin, there has not been any monitoring effort to determine the levels of their residues and their metabolites in the river to date. This study was therefore conducted in order to give an insight of the status of pollution by these herbicides and their stable degradation products along the river. Water, sediments and fish sample were collected at bi-monthly intervals from August, 1998 to February, 1999 from nine sampling sites along river Nzoia. Water samples were extracted using acetone and hexane solvent. extracted with dichloromethane and n-hexane by centrifuging Sediments were techniques while fish samples were subjected to soxhlet extraction ( Mann, 1995; UNEP, 1988). The extracts were cleaned and dried by passing through florisil and sodium sulphate respectively, and analysed by chromatographic methods using external standards to determine the quantities of these herbicides and their metabolites in the samples. 2-chloro-2' ,6' -diethyl-N-(methoxymethyl)acetaniline(alachlor), 2-chloro-N-(2- ethyl-6-methylphenyl)-N -(2 methoxy-1-ethyethyl)acetamide(metolachlor) metabolites; 2, 6 – diethylaniline and 2-ethyl-6 methylaniline detected in 51.58, 37.03 and 81.48% respectively analysed. In sediments, and the (DEMA) were of all the water samples 2-chloro-2' ,6' -diethyl-N-(methoxymethyl)acetaniline (alachlor) was detected in 51.58%, while 2-chloro-N-(2-ethyl-6-methylphenyl)-N- (2-methoxy-1 ethyethyl)acetamide(metolachlor) and DEMA were both detected in 70.37%. In fish, 2-chloro-2' ,6' -diethyl-N-(methoxymethyl)acetaniline (alachlor),