Effects of Ca~(2+) and Mg~(2+) on the toxicity of arsenate in a high arsenic coal mine area in southwest Guizhou

We studied the protective effects of Ca2+,Mg2+ against the toxicity of arsenate,which is widely present in water near the high arsenic coal mines in southwest Guizhou using Daphnia carinata as the test organism.The results showed that with arsenate single exposure,24 h,48 h,72 h and 96 h median lethal concentration(LC50) of arsenate to Daphnia carinata were 5.9817 mg·L-1,5.1800 mg·L-1,4.1884 mg·L-1 and 3.2015 mg·L-1,respectively.With Ca2+(20 mg·L-1,60 mg·L-1 and 100 mg·L-1) and arsenate co-exposure,the LC50 after 24 h were respectively 25.8449 mg·L-1,33.4735 mg·L-1 and 24.7439 mg·L-1 and the LC50 at 96 h were 4.9502 mg·L-1,5.7231 mg·L-1 and 4.5072 mg·L-1,respectively.With Mg2+(5 mg·L-1,10 mg·L-1 and 15 mg·L-1) and arsenate co-exposure,the LC50 of 24 h were 33.8412 mg·L-1,29.7261 mg·L-1 and 25.4113 mg·L-1,respectively and the LC50 of 96 h were respectively 6.8802 mg·L-1,4.9167 mg·L-1 and 3.0276 mg·L-1.Comparing to arsenate single exposure,the toxicity was lower at 24 h,48 h and 72 h when Daphnia carinata was exposed to a solution of arsenate and Ca2+ or Mg2+.After 96 h,the toxicity was relatively higher at low concentrations of arsenate(0~2.07 mg·L-1),but lower for high-concentrations of arsenate(3.70~20.72 mg·L-1).