Magnesium application reduced heavy metal-associated health risks and improved nutritional quality of field-grown Chinese cabbage

Magnesium (Mg) is one of essential plant nutrients needed for optimal growth, yield and quality formation. Also, soil application of Mg fertilizer has been shown to be an effective approach to improve vegetable Mg nutrition. Leafy vegetables can accumulate relatively high levels of heavy metals in the above-ground plant parts. However, it remains unclear as to whether soil-applied Mg affects the vegetable nutritional quality and human health risk of heavy metals from field-grown Chinese cabbage. Here we conducted a two-year, two-crop cycle field experiment in south-western China to evaluate crop yield, vegetable nutrition and heavy metal accumulation in Chinese cabbage supplied with varying levels of Mg (0-90 kg ha(-1)). Soil application of Mg did not increase the cabbage yield. However, it did increase the vegetable vitamin C and water-soluble protein content by 20.0 % and 57.9 % with 45 and 22.5 kg Mg ha(-1) application, respectively, compared to control. The nitrate content of Mg-supplied (45 kg ha(-1)) cabbages was significantly lower, by about 14 %, than the control. Further, it also significantly decreased the accumulation of cadmium and nickel in the above-ground tissues by reducing their uptake from soil to root or their translocation from root to shoot. Magnesium application, however, increased chromium uptake. A human health risks assessment nonetheless showed that the contribution of chromium from Mg-supplied plants to threshold hazard quotient and threshold carcinogenic risk were indeed much lower than that of cadmium and nickel, proving the value of crop Mg supplementation for ameliorating non-carcinogenic and carcinogenic risks to humans with the consumption of Chinese cabbage. Here we show that soil application of Mg in the range of 22.5-45 kg ha(-1) to Chinese cabbage will significantly improve its nutritional qualities and alleviate the potential human health risks of heavy metals associated with Chinese cabbage consumption.