A Risk Assessment of Reusing Wastewater on Agricultural Soils - A Case Study on Heavy Metal Contamination of Peach Trees in Ouardanine, Tunisia

Abstract: This thesis is a risk assessment of the risk related to ingestion of heavy metals via peaches irrigated with treated wastewater. The studied heavy metals were Cadmium (Cd), Lead (Pb), Zinc (Zn) and Cupper (Cu). The thesis is founded on a case study performed on a peach field in Ouardanine, Tunisia. Analysis of the heavy metal content in the treated wastewater used for irrigation was conducted as well as the heavy metal content in the field. Soil properties like pH, organic matter and particle size were analysed to achieve a picture of the heavy metals availability to translocate into plants. Heavy metal content in the peaches was measured and used to calculate the Hazard Index (HI) for consumption of peaches. The analysis showed that there were no significant amounts of heavy metals in the irrigation water. The field´s level of Pb, Zn and Cu were well within recommended limits for agricultural soils. The recommended level for Cd was below the detection level, and thereby it was hard to draw any conclusions. Cd level in the fruit was within the recommended limit. Pb was in some cases above the recommended limit, but as in the case with Cd in soil, the detection limit was above the recommended levels. The soil properties showed that the field is appropriate for reuse, as the properties reduce heavy metals ability to translocate to plants. HI was very low for consuming peaches from Ouardanine, thereby indicating a very low risk. According to this study, the irrigation water should not increase heavy metal accumulation in the peach field. However, sludge from the nearby treatment plant is used as fertilizer, and should therefore be a far more important source.