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

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.