Some Advantages of the Duckweed Test to Assess the Toxicity of Environmental Samples

In Germany, wastewater legislation requires all municipal and industrial leachate to be subjected to toxicity tests. However, no phytotoxicity tests using higher plants are currently included among the standard tests. Freshwater microalgae have been used in most phytotoxicity tests and have often been considered as surrogates for higher plants. However, microalgae often do not show the same sensitivity as higher plants and have major disadvantages for the testing of unmodified environmental samples. In the following study, we evaluated the suitability of the giant duckweed Spirodela polyrhiza for assessing the toxicity of a municipal landfill leachate and two leachates of copper mining residue. Duckweed static toxicity tests were performed, and frond number was the endpoint used to calculate EC₅₀ values. Symptoms of stress (chlorosis, necrosis, root destruction, and colony breakup) were also recorded. The landfill leachate was toxic with EC_50;96h values ranging from 1.3 to 2.7% leachate (v/v). Toxicity of the copper slag leachate was largely determined by the elution method used. Leachate obtained using conventional German leaching methods (S4-eluate) was not toxic to duckweed, whereas EC₅₀ values for the pH_stat4-eluate ranged from 3.2 to 4.2% leachate (v/v). The results demonstrate the suitability of S. polyrhiza for the testing of unmodified wastewater samples and provide further evidence for the addition of a duckweed toxicity test to the standard tests conducted in Germany.     

浮萍和水花生降盐碱的效果及其对水质的影响

于1998年7－8月间选取山东省高青县赵店乡大芦湖养殖内一口盐碱池塘的池水为试验用水，引进浮萍与水花生研究其降盐降碱作用以及它们对化学、生物因子的影响。结果表明：水花生没有明显的降盐碱作用；浮萍的降盐效果也不明显，但其降碱效果明显。同时会引起水体中中钙离子浓度下降和pH值的升高。另外，它们降低了水体中营养盐浓度和浮游植物生物量，但对浮游生物的多样性影响不大。