Toxicity of heavy metals and salts to eurasian watermilfoil (Myriophyllum spicatum L.)

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Abstract

The toxicity of various heavy metals and salts to Eurasian watermilfoil (Myriophyllum spicatum L.) was determined under controlled growth conditions. Toxicants were added to water or to soil in systems with and without woods earth in the substrate.

Fifty precent inhibition of root weight occurred with concentrations of 0.25 ppm Cu+2, 1.9 ppm Cr2O7 −2, 3.4 ppm Hg+2, 2.9 ppm AsO2 −1, 7.4 ppm Cd+2, 2.5 ppm Al+3, 9.9 ppm Cr+3, 41.2 ppm Ba+2, 21.6 ppm Zn+2, 13.3 ppm NH4 +1, 22.4 ppm CN−1, 143 ppm B4O7 −2, 363 ppm Pb+2, 10,228 ppm Na2SO4, and 8,183 ppm NaCl. Soil increased toxicity of Cr+2 and Ba+2 but decreased toxicity of Cr2O7 −2, Cu+2, Cd+2, Al+3, and Hg+2. In distilled water, CaCl2 increased toxicity of Cr+3 but not Cr2O7 −2.

For most toxicants there was a consistent relationship between inhibition of length and inhibition of weight and between inhibition of roots and inhibition of shoots. However, Cr2O7 −2 disproportionately decreased dry weight, and Hg+2 and Na2SO4 disproportionately decreased stem length growth. With Cd+2 and Cu+2 stem length was greater relative to other measures of growth. Toxicity of Na2SO4 and NaCl was the same when concentrations were calculated as osmotic pressure but not when calculated as Na atoms or as total molecules/L.