Impacts of wastewater irrigation on soils and crops in suburban area of Shiraz, Iran

This preliminary work reported here dealt with potential impacts of wastewater irrigation on soils and crops sampled along the Koshk River canal in the suburban area of Shiraz City, Iran. It also attempts to assess the extent of heavy metal contamination in soils and crops and human exposure risk. For this purpose, samples including soils and plants were collected from two wastewater irrigated sites and a tubewell-irrigated site （marked by A, B and C）. Concentrations of the six heavy metals Ni, Pb, Cd, Zn, Cr and Cu were determined by AAS. Physical and chemical properties of soil samples were also determined. The PLIs and CF for soils and HQ （Hazard quotient） for some vegetables were calculated. The results showed that organic matter content increased from 22% to 30 % in wastewater-irrigated soils as compared to tubewell water irrigated and admixture water irrigated ones. The soil pH was raised by 2 units as a result of wastewater irrigation at site A compared to sites B and C. Wastewater irrigation also result in relatively high concentrations of Ni, Pb and Zn （275.5, 441.3 and 177 mg/kg, respectively） in wastewater irrigated soils over tubewell water irrigated soils. These levels are higher than the maximum permissible limits in unpolluted soils, indicating that a degree of contamination has occurred. This was confirmed by calculated PLIs and contamination factors in soil samples, The results also showed some crops cultivated at sites A and B contained high levels of Ni and Cd beyond the maximum permissible concentrations and those cultivated at site C. The concentrations of these heavy metals are within or very close to the critical levels. HQ indices and daily intake calculated in respect of metal contents in some vegetables （spinach, lettuce and celery） showed that toxic risk due to Cd in these vegetables and crops was greater than one. This study generally concludes that although the content of heavy metals did not reach toxic level, extensive use of untreated wastewater drawn from the Koshk River has obviously increased the contamination of Ni and Pb in soils and Cd in some vegetables cultivated along the canal, causing potential health risk in the long-term scense for consumers or local residents.

Impacts of wastewater irrigation on soils and crops in suburban area of Shiraz, Iran