Differential Physiological Response and Potential Toxicological Risk of White Cabbage Grown in Zinc-Spiked Soil

Abstract

Physiological, agricultural and toxicological impact of an excess of Zn in the soil is an important issue, as Zn is a heavy metal and impairs many processes of plants and animals. The novelty of this work is that it is a comprehensive approach to facilitate visualization not only of the condition of cabbage plants under Zn stress, but also prediction of the toxicity associated with consumption of such cabbages. We treated plants of two cabbage cultivars, differing in their earliness, with 50 and 200 mg Zn kg−1 soil (Zn50 and Zn200, respectively) above the natural Zn levels of 118.13 mg kg−1 soil (Zn0). Leaf cell membrane integrity, condition of the photosynthetic apparatus (reflected by relative chlorophyll content (SPAD) and Fv/Fm parameter of chlorophyll a fluorescence), head biomass, and Zn bioaccumulation in the heads were analyzed. Toxicological risk was also assessed by Daily Intake of Metal (DIM) and Health Risk Index (HRI) indicators. The data revealed that plants of the late cultivar were more sensitive to soil Zn than those of the early one. Detrimental effects of Zn (especially at the higher dose, Zn200) were manifested in the seedlings just after three weeks of treatment, and then reflected in the yield. We assume that, due to their fast and prolonged response to Zn, the seedlings of the late cultivar can be used as biomarkers of Zn toxicity. Although Zn plants did not indicate toxicological risk, based on DIM and HRI, Zn concentration in the soil should be taken into account prior to cabbage planting, because plants which do not reveal symptoms of injury can accumulate Zn above the permissible level.