Cu and glyphosate toxicity to earthworm (Eisenia fetida)

Interactions of pollutions are among current research focus in environmental sciences. Fungicides contained copper (Cu) and herbicide glyphosate (GPS) are widely used in orchards and other agricultural ecosystems. Co-existence of Cu and GPS could result in combined pollution of soil environment. GPS affects metal behaviors in water and soil systems because its functional groups such as amine, carboxylate and phosphonate react with metal ions to form metal complexes. A laboratory experiment was therefore conducted to investigate the interactions of GPS and Cu with respect to sub-acute toxicity to soil invertebrate earthworms. Earthworms were exposed to spiked soil (70% garden mould and 30% dairy manure) for 35 d with different concentrations of Cu and GPS (technical-grade glyphosate acid). Deionized water was the blank control, Cu concentrations were 25 mg·kg^-1, 50 mg·kg^-1, 100 mg·kg^-1, 200 mg·kg^-1 and 400 mg·kg^-1 and GPS concentrations were 25 mg·kg^-1, 25 mg·kg^-1, 100 mg·kg^-1, 200 mg·kg^-1 and 500 mg·kg^-1 by soil dry weight in a single toxicity test. Simultaneously, two Cu levels of 25 mg·kg^-1 and 200 mg·kg^-1 were mixed by adding 0 mg·kg^-1, 25 mg·kg^-1, 50 mg·kg^-1, 100 mg·kg^-1 and 200 mg·kg^-1 of GPS in a complementary test. The purpose of the study was to address the possible inductions of earthworm (Eisenia fetida) exposure to single Cu and GPS and the corresponding interactions. The relative growth rate of earthworm biomass and Cu uptake were then measured. Results showed that the relative growth rate of earthworm biomass was significantly inhibited by high Cu concentration (α=0.01, r²=0.570). Furthermore, earthworm Cu content significantly increased with increasing soil Cu concentration (α=0.01, r² =0.905). GPS had no significant effect on the relative growth rate of earthworm biomass. The complementation test data showed that GPS significantly decreased earthworm Cu burden when soil Cu concentration was 200 mg·kg^-1. Higher acute toxicity was noted for Cu than for GPS. To a certain degree, GPS decreased toxicity. Thus GPS was recommended in controlling soil toxicity and bioavailability of soil heavy metals in conditions where both GPS and heavy metals co-exist.