Heavy metal toxicities: levels of nickel, cobalt and chromium in the soil and plants associated with visual symptoms and variation in growth of an oat crop

Abstract

A study was made of toxicity in a field crop of oats on a soil developed in an area where ultrabasic rocks occur. An area selected for sampling showed a range of toxicity from the border where plants were normal to the centre where plants were most affected. The total nickel, cobalt, and chromium contents of the soil increased to high levels at the centre of the area. The concentration of the elements in soil solutions extracted with a centrfuge from soils at field capacity were in the order nickel > cobalt > chromium, the order in which they are found in natural waters. In the soil solutions nickel ranged from 0.13 to 3.25 p.p.m., cobalt from 0.03 to 0.14p.p.m., and chromium from 0.01 to 0.02p.p.m. The concentrations found in the soil solutions were compared with concentrations known to induce toxicities in oats grown in frequently renewed solution cultures. These comparisons indicated that the nickel ranged up to levels which were definitely toxic. At its highest level cobalt was present at less than one-tenth of the level needed to induce toxicity, while chromium was present at only one-hundredth of the minimum level for toxicity. Analyses of the toys of plants from the centre of the area indicated values of chromium which would be considered toxic, but because of the very low concentrations of chromium in the soil solutions it was considered more likely that the chromium detected was in soil material which the acid detergent washing procedure failed to remove. Evidence presented indicates the particular importance of contamination in the case of chromium. Nickel was present in much higher quantities at toxic levels. Cobalt was below toxic levels. The symptoms observed in the field and symptoms induced by the application of nickel to oats in pot cultures are described. A feature of these symptoms was a regular succession of chlorotic bands. The evidence suggested that the banding pattern, which is best developed in clear weather, relates to the changing conditions which influence the actively growing tissue as the leaf is emerging. The symptom provided us with a means of identifying nickel toxicity in the field. Degrees of toxicity were related to levels of elements in soil extracts and in the plants.