Copper Uptake from Soil Treated with Sewage Sludge and its Implications for Plant and Animal Health

Abstract

Results of field and pot trials are reported which have examined the transfer into crops of copper added to soil in sludge. A pot trial with 39 different crops indicated which species are most sensitive to soil Cu and showed that plant genotype is an important factor determining the availability of Cu added to soil in sludge. In a field trial, less than 0.1% of Cu added to soil in sludge was recovered in the standing crop. An addition of 443 kg/ha of Cu in sludge increased the Cu concentration of herbage by 2.2 mg/kg to 6.8 mg/kg. In comparison, the phytotoxic threshold concentration of Cu in plant tissue is approximately 20 mg/kg and a level of 10 mg Cu/kg is required in the diet of ruminants. Uptake of Cu was greatest in the first year after application of sludge and declined thereafter. Significantly higher concentrations of Cu were found in ryegrass grown in pots compared with field plots which had received an equivalent amount of sludge. Results of pot trials must be interpreted with caution. It is concluded that Cu uptake from soil treated with sludge at rates associated with norml operational practice is unlikely to lead to deleterious effects on crop yield or the health of farm animals.