Toxicity of nickel to common duckweed (Lemna minor)

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Abstract
The nickel concentration of 1.0 mg/L in total form has been adopted as the indigenous aquatic life standard. The objective of this study was to test nickel toxicity to duckweed in water samples encompassing a wide variety of water quality. Fifty‐nine samples were collected from 18 stations: 10 in Illinois and 8 in neighboring states. Common duckweed, Lemna minor, was exposed to nickel for 96 h. Nickel exhibited the highest phytotoxicity to duckweed in water from the Hayes Creek and Horseshoe Lake stations, the two stations where water contained the lowest hardness, 37 to 78 mg/L as CaCO3. The IC50s for nickel were 0.36 and 0.21 mg/L, respectively. The other 16 stations, combined, showed a mean and standard deviation of 2.5 ± 0.83 mg/L. It is estimated that the nickel ion at a concentration of 1 mg/L can cause a 30% inhibition of duckweed growth in almost all surface waters, and a 70% inhibition in extremely soft waters.