Heavy metal accumulation in soil and leafy vegetables irrigated with domestic wastewater in Vietnam

This study was conducted to evaluate the accumulation of heavy metals, including copper (Cu), lead (Pb), and cadmium (Cd), in soil and leafy vegetables irrigated with domestic wastewater. The surveyed vegetables included water spinach (Ipomoea aquatica), Chinese mustard greens (Brassica integrifolia), and Malabar spinach (Basella alba), grown over three consecutive seasons. Results showed that Cu accumulation in the vegetables ranged from 4.41 mg/kg to 5.62 mg/kg, Pb from 0.11 mg/kg to 0.13 mg/kg, and Cd from 0.02 mg/kg to 0.03 mg/kg. All values were below the safety limits set by Vietnam’s National Technical Regulation (QCVN), with thresholds of 30 mg/kg for Cu, 0.3 mg/kg for Pb, and 0.2 mg/kg for Cd. Similarly, heavy metal accumulation in the soil remained within the permissible limits under QCVN standards. The analysis further indicated that seasonal variations had minimal impact on heavy metal concentrations, suggesting that consistent wastewater management practices contributed to maintaining soil and crop safety. In addition, the research highlighted that water spinach accumulated slightly higher levels of heavy metals compared to the other vegetables, likely due to its faster growth rate and higher water absorption capacity. Despite this, the concentrations remained well within safety thresholds, affirming the viability of these crops for safe consumption. The study concludes that using domestic wastewater for vegetable irrigation does not lead to heavy metal accumulation beyond safe thresholds, supporting sustainable and safe agricultural practices. However, continued monitoring and appropriate wastewater treatment remain essential to ensure long-term safety, particularly as environmental and anthropogenic factors evolve.