Phytoavailability of copper in the presence of recycled water sources

Background and aims: Recycled water irrigation provides a reliable source of water supply to farmers and also adds valuable plant nutrients and organic matter to the soil. However, untreated or partially treated wastewater can introduce inorganic and organic contaminants, including heavy metals, into agricultural lands. The objective of this study was to evaluate the transformation of copper (Cu) in soils treated with recycled water sources and its subsequent uptake by plants. Methods: The impact of recycled water sources [farm dairy effluent (FDE) and piggery effluent (PE)] on the transformation and phytoavailability of Cu was examined using two soils (Gawler and Adelaide Hills) which varied in their pH and organic matter content. The soils were spiked with varying levels of Cu (0-500 mg kg-1) in the presence of recycled water sources and MQ-water. The transformation of Cu was examined by monitoring the CaCl2 extractable free Cu2+ and pore water metal concentrations. The phytoavailability of Cu in the presence of recycled water sources was analyzed using Indian mustard (Brassica juncea var. Varuna) plants. Results: The recycled water sources significantly reduced the CaCl2 extractable and pore water free Cu2+ concentrations in soils, indicating a decrease in the labile fraction of Cu. The results indicated that increasing the level of Cu applied through recycled water sources and Milli-Q (MQ) water elevated Cu concentration in plants. However, at the same level of Cu application, plants took up less Cu from recycled water-amended soils than from MQ-water-amended soils. The effect was more pronounced in PE treated soils, with a reduction in Cu concentration in the plant tissues by 74.8% and 54% in GL soil, and 57.2% and 49% in AH soil at 100 and 500 mg kg-1 Cu levels respectively, compared to the Cuspiked soils in the presence of MQ-water. Conclusions: The results clearly showed that the presence of organic carbon in the recycled water was proved to be effective in reducing Cu phytotoxicity at high levels of Cu addition, indicating that the metal-organic complexes decreased the bioavailability of Cu to plants.