Effect of humic acids on the toxicity of pollutants to Chlamydomonas reinhardtii: Investigation by a microscale algal growth inhibition test

Dissolved humic substances (DHSs) are the major components of organic matter in the aquatic environment. DHSs are well known to considerably affect the speciation, solubility, and toxicity of a wide variety of pollutants in the aquatic environment. In this study, the effects of the toxicity of heavy metals and hydrophobic organic pollutants (HOPs) on Chlamydomonas reinhardtii in the presence of humic acid (HA) were examined by a microscale algal growth inhibition (μ-AGI) test based on spectrophotometric detection. To clarify the relationship between the chemical properties of HAs and the toxicity change of pollutants, eight HAs from different sources were prepared and used. HAs were responsible for mitigating the toxicity of Hg, Cu, pesticides (γ-HCH, 2,4-D, and DDT), and polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap), anthracene (Ant), and benzo[a]pyrene (BaP). In particular, an approximately 100-fold decrease in the toxicity of BaP was observed in the presence of 10 ppm HAs extracted from tropical peat. The results indicated that the carboxylic group content and the HA molecular weight are correlated to the changes in the heavy metal toxicity. For HOPs, the aromaticity and polarity of HAs are crucial for mitigating their toxicity. Furthermore, it was clearly shown that the lake water including a high concentration of DHSs collected from Central Kalimantan, Indonesia, reduced the toxicity of Hg and γ-HCH on Chlamydomonas reinhardtii.

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Comparison of general water quality of rivers in Indonesia and Japan

In Java and Kalimantan in Indonesia, river water plays important roles in human life; for example, for transportation, and economic activities of the inhabitants. However, industrial, agricultural and domestic water is discarded into rivers directly in many developing countries, including Indonesia, since drainage systems have not been completely constructed. In this study, to evaluate the water quality and to compare those levels of environmental contaminants in developing and developed countries, water quality and contents of endocrine disrupters were measured in a total of 64 water samples (Indonesia; 28 samples and Japan; 36 samples) from 53 sites. The results indicated that, rivers in both capital cities, Jakarta and Tokyo, were contaminated. Water in rivers in Indonesia was not so heavily polluted as in Japan. Pollution in the river water in Indonesia appeared to be caused by the lack of sewerage systems. In addition, the findings on endocrine disrupters indicated that the concentration of alkylphenol in water samples was large enough to affect living organisms.