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.

Toxicity thresholds for oat (Avena sativa L.) grown in Ni-impacted agricultural soils near Port Colborne, Ontario, Canada

“…It is notable that the soil Ni EC 25 s suggested by Anderson et al (1973) and Weng et al (2003) are similar to the regulatory criterion for Ni in soil in many jurisdictions, and lower than observed in the present study. The solubility product (an equilibrium constant describing the concentration of ions in a saturated solution of an ionic compound) of Ni hydroxide is 10 (17.2 (Baes and Mesmer 1976), which translates into an equilibrium concentration of Ni, at saturation of solubility, of 0.01 mg L (1 .…”

“…This is perhaps not too surprising, as the exchangeable Ca concentrations in the serpentine soils used in Anderson et al (1973) were low (less than 30% of total CEC), relative to what is common for nonserpentine soils (60Á80% of total CEC), thus potentially posing less competition for Ni uptake by plants ( Kinraide 1998;Parker et al 1998). The data of Weng et al (2003) suggest that the EC 25 for shoot biomass occurred at approximately 4 mmol Ni kg…”

“…Soil Ni concentrations associated with a 25% reduction in shoot height calculated from Anderson et al (1973) ranged from 78 to 266 mg kg…”

“…They determined that tissue Ni for oat at 25% reduction of shoot growth was 63 mg kg (1 , which is similar to those observed in this study for sand and heavy clay, but threefold greater than the tissue Ni EC 25 observed for till clay. From Anderson et al (1973), tissue Ni EC 25 were calculated to range from 43 to 88 mg kg…”

“…Because these soils are somewhat elevated in Cu concentration, which, along with high soil Ni concentration, can induce Fe deficiency in plants, tissue concentrations of Fe and Cu, as well as Mn (several of the soils in Port Colborne are Mn deficient) were considered in the interpretation of plant responses to elevated soil Ni. Although not an important agricultural species in Port Colborne, oat was chosen because of its known sensitivity to Ni (Hunter and Vergnano 1952;Anderson et al 1973), as well as the ease with which the development of readily visible chlorotic bands allow the recognition of Ni phytotoxicity. A range of soil Ni concentrations was achieved by blending field-collected soils instead of spiking uncontaminated soil with metal salts.…”