The effect of long-term wastewater irrigation on accumulation and transfer of heavy metals in Cupressus sempervirens leaves and adjacent soils

Abstract

Wastewater reuse for agriculture is an important management strategy in areas with limited freshwater resources, yielding potential economic and environmental benefits. Here the effects of long-term irrigation with wastewater on the nutrient contents of green and senesced leaves of Cupressus sempervirens L. were assessed for three planted forests in Egypt. Stoichiometric ratios, transfer factors for nutrients from soil to plant and enrichment factors in contaminated soils were estimated and compared to a ground water irrigated control site. Under wastewater irrigation, C. sempervirens transferred most of the estimated nutrients, particularly heavy metals, from green to senesced leaves. This could be a self-protecting mechanism under continuous wastewater irrigation. The accumulation of four metals (Zn, Mn, Cu and Cd) with transfer factors>1 for wastewater-irrigated trees, indicated the ability for metal accumulation of C. sempervirens. Stoichiometric ratios decreased under wastewater irrigation compared to the control site and global trends, which suggests nutrient disorders in these plants. The values of enrichment factors in the wastewater-irrigated soils showed remarkable availability and distribution of metals. Decreased resorption of metals by senesced leaves of C. sempervirens will add considerable amount of these metals to the soils, which will likely have adverse affects on the desert ecosystem components.

Keywords: Cupressus sempervirens; Heavy metals; Macro-nutrients; Senesced tissues; Transfer and enrichment factor; Wastewater irrigation.