Levels and Potential Sources of Heavy Metals in Major Irrigated Rice Areas of the Philippines

Abstract

Industrialization, urbanization and intensive use of farm inputs can pollute agricultural areas. The study was then conducted to assess the levels of chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co), zinc (Zn), arsenic (As), molybdenum (Mo), cadmium (Cd), mercury (Hg), and lead (Pb) in the country’s major rice areas. The study also determined the contributions of soil properties, land uses, irrigation water, and farm inputs to the metal levels. Strategic collections of soil, plant and water samples in the country’s major soil series planted to rice, analyses of samples using x-ray fluorescence or atomic absorption spectroscopy, and farmer interviews were done. Metal levels were very high in Zambales and Negros Occidental soils due to deposition or use of metal-enriched mine tailings and irrigation water. Soil metal concentrations in Zambales far exceeded the intervention values of 180 mg/kg for Cr and 100 mg/kg for Ni. Soil metal levels in Negros Occidental exceeded the intervention value of 190 mg/kg for Cu and Mo. Rice plants in Negros Occidental exceeded the toxic levels of 30 mg/kg for Cu and 10-50 mg/kg for Mo due to the very high soil Cu and Mo concentrations in the area. Molybdenum concentrations of rice plants in Sultan Kudarat and Camarines Sur exceeded the toxic level due to the high amounts of foliar chemicals applied at >66 sprayer loads per year. The study implies that rice areas deposited with mine wastes have high heavy metal levels, and foliar chemicals can increase metal levels in rice. Keywords - Environmental toxicology, heavy metals, heavy metal sources, rice soils, Philippines

Zinc and Iron Nutrition Status in the Philippines Population and Local Soils

“…Zn-deficient paddy soils were identified for rice plants based on the results of the Minus-One Element Technique (MOET) followed by Descalsota et al (137). A significant positive correlation and linear regression between soil Zn and plant Zn were observed by Magahud et al (25), indicating that higher soil concentrations of Zn lead to higher Zn concentration in rice plants. The concentration of Zn in rice, particularly in the grains, is highly affected by the amount of bioavailable Zn in the soil (117, 130).…”

“…In another study conducted by Magahud et al (25), which assessed the levels of heavy metals, including Zn, in the country's major rice production areas found that Zn concentrations are generally low in rice production areas. Figure 2 presents the results of the studies on the concentrations of micronutrients, particularly Fe and Zn.…”

“…Micronutrient concentrations of major rice paddies in the Philippines (24, 25) in various regions in the country, with each bar representing different sample sites (provinces), showing deficiency in Zn based on (a) Canadian soil guidelines for agricultural soils and (b) Netherlands target values for soils. The concentration of nutrients is measured in ppm.…”

Spatial distribution of agricultural yields with elevated metal concentration of the island exposed to acid mine drainage

“…This leads to land degradation and affects the agricultural land use. This condition was also discussed in the work of Barman et al (2000); Intangwogse and Dean (2007); Kumar, (2013); Magahud et al (2015); Marquez et al (2018). These works were carried out 'in-vitro', applied research in Philippines (specifically in Zambales and Negros Occidental) and Vietnam, respectively.…”

Spatiotemporal Variation of Groundwater Arsenic in Pampanga, Philippines

“…The majority of stream sediment samples (N = 39) collected from the Zambales Mountain Range in Central Luzon contained 0.05-1.0 ppm As, while the highest measured was 114.8 ppm [8]. A study on rice paddy soil samples revealed As values beyond the soil background value of 9.0 ppm in some parts of Laguna (15.5 ppm) and Camarines Sur (9.2 ppm) in Luzon and Negros Occidental (11.4 ppm) in Visayas [9]. Groundwater samples from Central Luzon were found to contain As beyond the 2017 Philippine National Standards for Drinking Water (PNSDW) limit of 10 ppb, with values as high as 300 ppb [7].…”