Accumulation and bioavailability of Cd, Co and Mn in soils and vegetables irrigated with city effluent

Untreated city effluent is used for growing vegetables around big cities in most parts of the country. We determined the irrigation quality of city effluent and its impact on soils and vegetables' quality. This study was conducted at sites: Kernailwala (site I) and Judgewala(site II) within the Municipal limit of Faisalabad. Effluent samples were collected from the sites fortnightly from June 1998 to June 1999. Soil samples were drawn from 0.00-0.20, 0.20-0.40, 0.40-0.60, 0.600.80 and 0.80 to 1.00 m depths and were analysed for physical and chemical properties, and for heavy metals like Cd, Co and Mn. Associated vegetable samples (leaves and fruits separately) were collected from the same fields for their heavy metal contents. Quality of the effluent was marginal at site I [EC 1.1-1.7 dS rn', SAR 5.9-17.4 (mmol L'1)1/2and RSC 1.0-2.1 mmol, L'1j and unfit for irrigation at site II (EC 3.7-4.1 dS rn', SAR 16.1-21.9, RSC 4.0-9.1 rnrnol, L'\ Concentration of AB-DTPA extractable Cd, Co and Mn for 0-20 cm soil depth was 0.080,0.057 and 216.62 mg kg'1 at site I while the corresponding values were 0.104, 0.077 and 176.96 at site II. In soils irrigated with city effluent, Cd and Co were found within safe limits but Mn was found above permissible limits. The concentration of Cd, Co and Mn tended to decrease with an increase in soil depth. Higher accumulation of metals was observed in plant leaves than their respective fruits. Manganese concentration in plants was much higher than those of Cd and Co. Edible parts of vegetables (fruits or leaves) grown with city effluent accumulated metals beyond permissible limits in spite the soils contained metals within permissible range, particularly where leaves are consumed. This is a continuous and serious hazard to soils and plants and ultimately to human health suggesting that either the practice must be discouraged or must be followed with appropriate/scientific management. Specific disorders due to toxic levels of different metals have also been highlighted.