The toxicity of water samples taken in the streams at the mine to
algae and daphnia is shown in Table 7. Toxicity to daphnia was observed
in all samples, causing 100% immobilization in all individuals, even in
sample A9, sited at the farthest point. Effects on algae were different
depending on the sample. The worst effects were observed in samples
A1 and A2 near the mine pit with a percentage of growth inhibition of
100%. Samples A3, A4 and A5 exhibited an inhibitory range between
75±11% and 94±5%, respectively, whereas sample A9 did not impair
algal growth. The response to samples A1 and A2 could be due to
the low pH (4.16 and 4.34) of these water samples. However, assays
performed with diluted samples indicated that effects were due to
contaminants in the samples rather than pH, as shown below.