Uptake and toxicity of nickel and other metals in crops grown on soil contaminated by a nickel refinery

Severe contamination of vegetation and soil by nickel, copper, and cobalt has been observed in the vicinity of a nickel refinery in Southern Ontario. Nickel concentrations in excess of 26000 parts per million (PPM) have been found in surface soil near the refinery and soil concentrations exceeding 100 ppm Ni are found over 8 km downwind of the refinery. Foliage samples from trees growing within 1 km of the refinery frequently exceed 200 to 300 ppm Ni, with lesser amounts of Co and Cu. Despite these high concentrations of Ni, overt metal toxicity symptoms are confined to a few extremely susceptible native species such as silver maple (Acer saccharinum L.), and to susceptible crops such as oats, lettuce, and cabbage. Uptake and toxicity of Ni and other metals were studied in crops growing on a muck farm located about 1 km east of the refinery, where the Ni content of the organic soil ranged from approximately 2000 to 10000 ppm. Growth of crops such as onions, potatoes, celery, cabbage, and lettuce was severely inhibited at 10000 ppm Ni and severe toxicity symptoms were observed. Growth was more or less normal at 2000 to 3000 ppm Ni. In a greenhouse bioassay study using metal‐contaminated soil, growth and yield of lettuce was reduced by 20 to 35%, and stalk weight of celery was reduced by 35%, compared with growth in control soil. Lettuce leaves grown on soil containing around 7000 ppm Ni averaged 84 ppm Ni (dry weight); celery stalks averaged 29 ppm Ni, and onion bulbs averaged 47 ppm Ni. The pH (5.6 to 6.7) and high organic matter content (>40%) of the soil on the muck farm reduced the potential toxicity to crops of the extremely high metal levels in the soil.