The Impact of Agricultural Runoff on the Quality of Two Streams in Vegetable Farm Areas in Ghana

Abstract

A study of two small streams at Akumadan and Tono, Ghana, was undertaken during the rain and dry season periods between February 2005 and January 2006 to investigate the impact of vegetable field runoff on their quality. In each stream we compared the concentration of current-use pesticides in one site immediately upstream of a vegetable field with a second site immediately downstream. Only trace concentrations of endosulfan and chlorpyrifos were detected at both sites in both streams in the dry season. In the wet season, rain-induced runoff transported pesticides into downstream stretches of the streams. Average peak levels in the streams themselves were 0.07 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Akumadan stream); 0.04 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Tono stream). Respective average pesticide levels associated with streambed sediment were 1.34 and 0.32 microg kg(-1) (the Akumadan stream), and 0.92 and 0.84 microg kg(-1) (the Tono stream). Further investigations are needed to establish the potential endosulfan and chlorpyrifos effects on aquatic invertebrate and fish in these streams. Meanwhile measures should be undertaken to reduce the input of these chemicals via runoff.

Pesticide Contamination in Groundwater and Streams Draining Vegetable Plantations in the Ofinso District, Ghana

“…The average pesticide application rate is estimated to be 0.08 litres active ingredient (a.i.) per hectare (Ntow et al, 2008). Misapplication and intensive use of pesticides in vegetable cultivation can result in pesticide contamination of the environment.…”

“…The extraction and analyses of water samples were performed following the Association of Official Analytical Chemists 990.06 and 970.52 methods as described by Ntow et al (2008). Briefly, water samples were extracted sequentially three times with 25 mL n-hexane each time.…”

“…Each eluate was evaporated and the extracts (re-dissolved in 1.5 ml n-hexane and made up to 2 ml with more n-hexane) were injected into a gas chromatographic system for identification and quantification of the pesticides. Extraction and analysis of sediment samples followed the method described by Ntow et al (2008). Briefly sediment samples were well mixed to obtain a homogeneous sample and then transferred into a pan to air-dry at ambient temperature until a constant weight was obtained.…”

“…Water content (expressed as weight fraction of water) was determined by first weighing wet sediment samples, then ovendrying the sediment samples at 105°C until constant weight, and obtaining the weight difference. Total suspended solids and turbidity were measured concurrently (Ntow et al, 2008). Total organic carbon was obtained from the percentage organic matter in the sediments as percentage loss-on-ignition after drying 1.0 g of the sediment samples (previously acidified for the removal of carbonates) at 550°C in a furnace (Mwamburi, 2003).…”

“…extensive network of drainage systems through which surplus water may flow out (Ntow et al, 2008). Vegetables cultivated in Ghana include tomato (Lycopersicon esculentum), eggplant (Solanum melongena), pepper (Capsicum annum) and onion (Allium cepa), although some regions are more efficient and specialised in the production of only one or two vegetable crops (Ntow, 2001).…”