Heavy metals in citrus fruits as affected by primary treated sewage irrigation

Abstract

This work aims to investigate the distribution pattern of heavy metals in the different parts of citrus trees. Monthly samples of different types of irrigation water (treated wastewater, groundwater, and fresh canal water) were collected. Both physicochemical characteristics and heavy metal concentration were evaluated. Different citrus plant samples and fruits from three different species of citrus trees were collected from the sewage farm as well as the farms irrigated with groundwater and canal water. All citrus tree samples were partitioned into: Leaves, stem and citrus fruit. The fruits were divided to the outer crust, and squeezed juice. The results showed that the level of metals in treated wastewater was within the permissible limits; while the citrus trees irrigated by this water contains higher levels due to metals accumulation. One important notice is that the toxic metals including Cd, Pb, Ni, Cr in all cases were at the lowest and/or below detection limit, particularly, in the citrus juice. The outer crust of the citrus fruits contained the second lowest level of all metal. Thus, the citrus fruits showed no accumulation of heavy metals. This could be explained by the fact that heavy metals were up taken by the roots and only smaller fractions were trans-located to the other parts of the tree. The essential nutrient metals including Fe, Mn, and Zn were accumulated mostly by leaves and stems. It was concluded that heavy metal accumulated differently according to the plant species, the part of the tree and fruit. Such fluctuations are governed by the irrigating water, pH of the soil, plant uptake and/or water-soil-to-plant transfer factors. Other factors include temperature, moisture, organic matter, phosphorous content and the availability of the other nutrient elements. The present experimental study showed that the primary treated wastewater should not be used for irrigating any edible plant.