Effects of iron sulfate dosage on the water flea (Daphnia magna Straus) and early development of carp (Cyprinus carpio L.).

摘要

Adult water fleas, Daphnia magna Straus, and the early life stages of carp, Cyprinus carpio L., were exposed to river water near an iron sulfate dosage installation to determine the effects of phosphate precipitation with iron(II)sulfate. Tests were conducted during two consecutive dosage periods of 3,000 and 5,000 kg/day iron sulfate (520 and 620 microg/L total Fe respectively) at the dosage site and at a reference site (60 microg/L total Fe) further downstream. Though survival remained unaffected, the filter-feeding D. magna accumulated iron and other metals at the dosage site. Viability of offspring was strongly reduced at the highest dose of iron sulfate compared to the lower dose and the reference site. Specific staining of microscopic sections revealed a strong accumulation of iron(III) in the digestive tract. The egg membranes of the carp embryos accumulated not only substantial amounts of iron but also other metals, including cadmium and aluminium. Hardly any of the metals passed the egg membranes and reached the embryos. After hatching the accumulation of cadmium by the larvae increased rapidly and iron levels were elevated at the highest dose of iron sulfate, parallel with the onset of exogenous feeding. Iron(III) particles were observed in the intestines at histological examination. In addition, at 620 microg/L total Fe a strong increase in whole-body levels of the stress hormone cortisol was observed in the carp larvae, indicating a physiological response to adverse conditions. The results indicate that the rapid oxidation of free Fe2+ into iron(III) forms and the precipitation of iron(III) into larger particles resulted in a low acute toxicity of the river water directly at the iron sulfate dosage site. The observed chronic and sublethal effects at the dosage site probably resulted from the intestinal uptake of iron(III) and other toxic metals associated with the food particles. However, these effects could no longer be observed at the reference site, 9 km downstream from the dosage site.