Heavy metal pollution in drinking water - a global risk for human health: A review

Water resources in the world have been profoundly influenced over the last years by human activities, whereby the world is currently facing critical water supply and drinking water quality problems. In many parts of the world heavy metal (HM) concentrations in drinking water are higher than some international guideline values. Discussing about the HM pollution in drinking water, the incorporation of them into the food chain, and their implications as a global risk for the human health, are the objectives of this review. It is known that there are million people with chronic HM poisoning which has become a worldwide public health issue, while 1.6 million children die each year from diseases for which contaminated drinking water is a leading cause. There is also evidence of HM in drinking water that are responsible for causing adverse effect on human health through food chain contamination. A global effort to offering affordable and healthy drinking water most to be launched throughout the world, while various laws and regulations to protect and improve the utilization of drinking water resources should be updated or created throughout the world, including the low income countries; otherwise, the problem of HM-polluted drinking water will be growing because demand for drinking water is still growing such as this problem will become even more pressing in the future. Finally, notwithstanding, additional researches are necessaries about the correlation between HM concentration in drinking water and human diseases, while the development of robust, cheap and sustainable technologies to improve the drinking water quality is necessary.Key words: Groundwater, aquifer, water quality, water pollution, microorganism, water supply, microbial communities, food chain, disease

Effect of pest-controlling neem and mata-raton on bean growth, soil N and soil CO2_{2} emissions

Extracts of plants such as neem (Azadirachta indica A. Juss.) and mata-raton (Gliricidia sepium (Jacquin)) are used to control pests. However, certain components of neem, such as azadirachtin, can exert a negative effect on fungi and nitrifying bacteria, and, in turn, can impact the C and N cycles in soil. Nutrient cycling might thus be inhibited and affect the sustainability of an agricultural system in which plant extracts are used to control pests. Here, we investigated the effect of neem extract on microbial activity and N mineralization in soil. We studied the effect of neem and mata-raton leaf extracts on bean growth (Phaseolus vulgaris L$.)$, nodule formation by Rhizobium, soil CO$_{2}$ emissions and soil N dynamics. Four treatments were applied: (1) "neem treatment": extracts of neem leaves, (2) "mata-raton treatment": extracts of mata-raton, (3) "chemical treatment": a chemical insecticide, lambda cyalothrin, and (4) "control": untreated plants. Our results show that in non-amended soil the number of nodules in the neem treatment was 18 for beans cultivated. This nodule number was 2.1 times lower compared with the soil treated with lambda cyalothrin (chemical treatment). In manure-amended soil, the number of nodules was 28 in the neem treatment. This nodule number was 1.6 times lower than in the mata-raton treatment. This indicated that neem extracts inhibited Rhizobium in soil and nodule formation in bean. In the manure-amended soil, the emission of CO$_{2}$ was 1.9 times lower in the neem-treated soil than in the other treatments. The increase in the concentration of NO$_{3}^{-}$ was 1.03 mg N kg$^{-1}$ soil day$^{-1}$ in the neem treatment and 4.1 times lower compared with the other treatments. As such, microbial activity was inhibited by the neem extracts when added to the manure-amended soil. It was found that application of neem leaf extract inhibited microbial activity and reduced nodule formation in bean, but lambda cyalothrin or leaf extracts of Gliricidia sepium did not