The problem of high levels of nickel in soils and plants in the ultramafic area in Samar, Philippines
One of the heavy metals that commonly occur in elevated amounts in natural ecosystems is nickel (Ni). Ni is considered an essential micronutrient for plants, humans, and animals. It can exist in trace amounts in air, food, drinking water, and soils. Although Ni plays an important role in the metabolism of humans and animals, its intake in excesssive amounts or over a prolonged period could pose health ricsks. Studies have shown that children living in polluted areas have hypertrophy of tonsils, enlarged lymphatic nodes, and enlarged livers. There is also evidence that soluble Ni particulate is linked to acute lung injury.
High Ni levels in natural ecosystems commonly come from ultramafic rocks (also called ultrabasic rocks). These are intrusive igneous rocks containing less than 45% silica (SiO2) with high concentrations of Ni, Mg, Fe, Cr, and Co. They are found in many places around the world and are common in many places in the Philippine like in Salcedo in the island of Samar.The watershed has a highly weathered soil (Oxisol) derived from the weathering of ultramafic rock. Previous studies conducted in the watershed revealed excessive levels of Ni, Cu, and Cr in the soil. Many farmers also complain of unexplained health problems which may be related to heavy metal toxicity.
In a study conducted in the Salcedo watershed and recently published in the international scientific journal Environmental Monitoring and Assessment, Susaya and co-workers (Susaya et al., 2009) evaluated the degree of Ni contamination in soils and plants in the watershed. The plants sampled included native species (non-food) such as Phyllanthus amarus, Melastoma affine, and Stachytarpeta jamaicensis as well as cultivated food crops like Calocasia esculenta, Citrullus vulgaris, Artocarpus heterophylla, Moringa oleifera, Psidium guajava, Lycopersicon esculentum, and Solanum melongena.
Reference
Susaya JP, KH Kim, VB Asio, ZS Chen, and IA Navarrete. 2009. Quantifying nickel in soils and plants in the ultramafic area in Philippines. Environmental Monitoring and Assessment (now available online at http://www.springer.com/environment/environmental+toxicology/journal/10661)
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