Cadmium in soil–rice system and health risk associated with the use of untreated mining wastewater for irrigation in Lechang, China

Using untreated mining wastewater to irrigate paddy field around Lechang lead/zinc mine in the upper Wu Jiang River basin, Guangdong Province, southern China, caused cadmium transport onto paddy soils and crop contamination. This study characterized Cd concentration in soil–rice system irrigated with the wastewater mentioned above and evaluated potential ecotoxicological hazardous risk to humans and animals. All soil and plant samples were analyzed using atomic absorption spectrophotometer (AAS; Model 3030, Perkin-Elmer, USA). The results showed that all soil samples were extremely contaminated by cadmium, soil Cd occurred primarily in the residual fraction. Using synthetic stomach fluid simulating gastrointestinal condition, result showed that 28.4% of the total soil cadmium concentration would be ingested in human/animal gastrointestinal tract. Mean Cd concentrations in plant tissues (DW) ranged from 0.24 (unpolished rice) to 8.21 μg g−1 (root). Dietary intake of cadmium through contaminated rice consumption was calculated to be 2.2 and 1.5 μg kg−1 body weigh per day for a 60-kg adult and 40-kg child, respectively. The values were much higher than the provisional tolerable daily intake (PTDI; 1 μg kg−1 body weight by FAO/WHO in 1989). Present results indicated that the paddy soil–rice system irrigated with untreated mining wastewater in Lechang lead/zinc mine area was heavily contaminated by Cd and would pose a human/animal health risk through Cd mobility in the food chain. Therefore, local mine wastewater should be decontaminated before being irrigated to surrounding farmland.