Evaluation of cadmium bioaccumulations in Pak Choi grown by hydroponics system

Abstract

Cadmium is one of the most harmful heavy metals reported to contaminate the food chain and pose a high risk for health, including non-carcinogenic and carcinogenic effects. High levels of cadmium contamination due to industrial effluent discharge have been reported to affect plant growth and productivity, which could be used as a bio-indicator for cadmium bioaccumulation in plants. The utilization of cadmium-contaminated water for vegetable production has been known to increase the health risk for human consumption. Moreover, pH level was known as a factor affecting cadmium solubility and cadmium uptake by plants. However, there is still unknown about critical pH level that is associated with high cadmium concentrations in water resources used in agriculture (e.g., river, lake, effluent, etc.) and results in bioaccumulation and health risk of vegetable consumption grown by the cadmium contaminated water. In this study, pak choi as a model plant in a hydroponic setup was used to access cadmium bioaccumulation and the health risk of vegetable consumption. The experiment was conducted using four initial cadmium doses (control: 0 mg/L, 1 mg/L, 2 mg/L, and 3 mg/L) in a four-week operation. Three initial pH levels (7.5, 6.5, and 5.5) were used for experiments I, II, and III, respectively. The study was designed to use nitrogen and phosphorus levels at low concentrations (ammonium = 0.91 ± 0.36 mgN/L, nitrate = 0.50 ± 1.4 mgN/L, phosphate = 0.23 ± 0.10 mgP/L), which were in range of wastewater effluent and natural water for agricultural reuse. Results show that cadmium concentrations of 1-3 mg/L significantly inhibited pak choi growth (p < 0.05) compared with the control. Bioaccumulation in plant roots (0.035–2.963) and leaves (0.434–1.038) occurred with an increase in cadmium concentration (p < 0.05), suggesting that cadmium ions were translocated from water to roots and accumulated in the edible part of pak choi (leaves and stems). The highest cadmium available in water (2.67 ± 0.1 mg/L) was found at the initial pH of 5.5 due to the solubility of cadmium at the acidic pH level. Based on US EPA average daily intake and health risk assessment, it was found that consumption of pak choi grown by the cadmium contaminated water resource in the range of 1 to 3 mg/L will not cause chronic non-carcinogenic (hazard quotient <1) but can cause carcinogenic effect (cancer risk > 10-6) over 30-year consumption. Therefore, it is recommended that the monitoring of cadmium in water for agricultural use must be regulated strictly.