Abstract
Farmers in peri-urban areas use diluted wastewater for irrigation. Over time, heavy metals may accumulate in agricultural soils and food crops causing health problems when consumed. Physicochemical, heavy metals (cadmium, lead and chromium) and microbial analysis of water, soil and vegetables were conducted to ascertain the quality of water and vegetables using standard methods. The results of the study showed that the water quality indicators; dissolved oxygen, biochemical oxygen demand and water temperature were not within the recommended standards of Ghana’s Environmental Protection Agency. The presence of heavy metals in the water, soil and vegetables were in the order of; soil (1.47 ± 0.017 of cadmium, 0.0019 ± 0.00011 of chromium and 0.541 ± 0.017 of lead) > vegetable (1.472 ± 0.044 of cadmium, 0.0020 ± 0.00010 of chromium and 0.474 ± 0.021 of lead) > water (0.068 ± 0.009 of cadmium, 0.0047 ± 0.00037 of chromium and 0.110 ± 0.014 of lead). Cadmium, chromium and lead concentrations in soil, vegetables and water varied significantly. Cadmium and lead concentrations as well as coliform counts in water and vegetables exceeded Food and Agriculture Organization/ World Health Organization’s maximum permissible levels. Soil samples from the control site showed almost negligible concentrations of heavy metals (0.00017 mg/kg of cadmium, 0.00014 mg/kg of chromium and 0.0011 mg/kg of lead) whereas farm sites had heavy metals as a result of long-term wastewater irrigation. Cadmium and lead concentrations in the water and vegetables makes them toxic and microbial populations of faecal coliform in water and lettuce indicated faecal contamination. Therefore, the quality of vegetables produced using the Bibini river is low and unsafe for human consumption.
Highlights
The pH and total dissolved solids were measured within 24 hours and the biochemical oxygen demand obtained after 5 days
Variables described include dissolved oxygen, temperature, pH, dissolved solids and biological oxygen demand, and represents analysis of samples taken from the entry point of effluent into river and subsequently after every 50 m interval
Heavy metals (Cd, Pb and Cr) are present in the water, soil and vegetables with cadmium and lead found in vegetables at concentrations above the permissible levels
Summary
In Ghana, urban and peri-urban agriculture is developing wherever land is available close to streams and drains (Obuobie et al, 2006). In Kumasi for example, informal irrigation, which uses stream water is estimated to cover 11,500 ha, which is twice the total area under formal irrigation in the whole country (Keraita and Dreschel, 2004). Buckets, motorized pumps with hosepipe and surface irrigation are used to fetch, pump and water crops. Surface water used for irrigation is usually of low quality due to human activities which introduces metals and other pollutants into the water (Dyjak, 2018). Heavy metal pollution originates from sources like untreated domestic and industrial waste discharges, accidental chemical spills, direct soil waste dumping, and residues from agricultural inputs namely fertilizers and pesticides (Tchounwou et al, 2012; Mico et al, 2006). Bio-accumulation of heavy metals occurs over time after entering the body through food, water or air
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