Toxic effects of low pH on Daphnia magna embryos

Abstract

This study focused on the toxic effects of low pH on Daphnia magna embryos, young, and adults in a soft and a hard water. Fourto six-hour-old embryos after egg laying were obtained from the female’s brood chamber and immediately exposed to four or five level of different low-pH solutions for 120 hours. Embryonic toxicity was determined by evaluating inhibition of hatching and immobilization of the embryos following 72, 96, and 120 hours of exposure to low-pH solutions. Young(<24 hours following release from the female)and adults were also exposed to four or five level of different low-pH solutions for 48 hours. Low pH resulted in significant toxicity during embryonic development, as was indicated by inhibition of hatching and/or immobilization in embryos following exposure to pH 6.6 in soft water and to pH 6.0 in hard water. Immobilization was observed in young when subjected to solutions at/below pH 6.5 in soft water and at/below pH 5.2 in hard water. Adults were more tolerant to low pH in soft water than young or embryos, with the pH causing 50% immobilization in adults following 48-hour exposure 1.4 points lower than that which resulted in young or embryos 50% immobilization. The hardness of the water in low-pH solutions can influence the immobilization ratio of young. These observations suggest that the embryonic developmental test in early life stages allows for rapid and sensitive determination of low-pH toxicity.