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

Nutrient levels in rice areas can be translated to the soils' capacity to supply the essential elements for rice, while information about nutrient sources can be used to formulate management options to areas deficient or toxic in nutrients. This study was then conducted to assess the potassium (K), calcium (Ca), sulfur (S), iron (Fe) and manganese (Mn) levels in the Philippines' major rice areas. The study also determined the contributions of soil properties, land uses, irrigation water, and farm practices to the nutrient levels. Strategic collection of soil and plant samples, laboratory analyses of samples, and farmer interviews were done. Potassium concentrations of rice plants in La Paz (Tarlac) and Sta. Rosa City (Laguna) exceeded the toxic concentration of 3%. These K concentrations can be due to the increase of the nutrient's availability owing to the neutral soil pH levels in the two sites. The highest total Ca levels were found in the Polangui (Albay), La Paz, and Villasis (Pangasinan) soils. These Ca levels can be ascribed to the occurrence of Ca in sand and silt-sized soil fractions. Total Fe and Mn concentrations were very high in the Sta. Cruz (Zambales) soil due to the input of mine wastes. The San Leonardo (Nueva Ecija) soil's high total Fe concentration is probably due to the occurrence of Fe in clay-sized soil fractions. Iron and Mn levels of rice in most Central Luzon sites exceeded the toxic concentrations of 1000 mg kg-1 for Fe and 300 mg kg-1 for Mn. These concentrations can be due to the high total soil Fe and Mn levels, and their increased plant uptake due to periodic soil submergence and increased soil acidity from continuous cropping. The study implies that K, Ca, Fe and Mn are enriched in rice areas due to soil properties and farm practices.

Information about pesticide application is relevant in assessing the risks of farmers’ exposure to pesticides and in crafting measures toward reduced pesticide use. A study was then conducted to assess the extent and frequency of application, and active ingredients of pesticides in thirty irrigated rice areas of the Philippines. The study was also done to determine factors that affect pesticide application relative to farmers’ perceptions, management practices, and the farms’ agroclimatic characteristics. A questionnaire was used to survey farmers’ application of chemicals against birds, rats, golden apple snails (GAS), weeds, and fungal diseases. Most farmers did not apply pesticides to reduce perceived bird and rat damages in their rice farms because they preferred non-chemical means of control. Most farmers applied chemicals to manage GAS and weeds that damaged or competed with rice. Molluscicide application was more frequent in Bicol sites with climate and soil characteristics that favor ponding of water. Frequency of herbicide application can be attributed to the direct seeding method of crop establishment. Most farmers did not encounter fungal diseases. Most widely used active ingredients are butachlor, niclosamide, and methaldehyde, which are slightly hazardous, unlikely to cause hazards, and moderately hazardous, respectively. This study suggests that molluscicide and herbicide applications are very common among Filipino farmers, which can be harmful to their health.   Keywords - Environmental Toxicology, pesticides, birds, rats, golden apple snails, weeds, irrigated rice, descriptive design, Philippines

Concentrations of strontium (Sr), rubidium (Rb), titanium (Ti), and zirconium (Zr) are relevant to agricultural, environmental quality and health and disease investigations. A study was then conducted to assess them in rice areas and determine the sources of high element levels relative to soil properties, land uses, irrigation water, and plant uptake. Thirty-two (32) soil and plant samples were collected in agricultural areas of the Philippines representing the major soil series devoted to irrigated rice production. Soil Sr levels were higher than the world average of 175 mg/kg. The highest Sr levels were found in Polangui (Albay), Tacurong City (Sultan Kudarat), and Sta. Cruz (Laguna). These Sr levels can be due to the soils’ high sand or available phosphorus (P) contents as Sr occurs in sand-sized soil fractions, and its sorption in soils is enhanced by high phosphate concentrations. Soil Rb levels in Kabacan (North Cotabato) and San Miguel (Iloilo) were higher than the range for Philippine rice or paddy soils (0–29 mg/kg). The level in San Miguel can be due to the soil’s high available P and neutral pH while the level in Kabacan can be due to the soil’s clay texture in its lower horizons. Titanium levels were highest (>205 mg/kg) in rice tops collected from Muñoz City (Nueva Ecija), but the reason for such high levels needs further investigations. Zirconium levels were highest (>18 mg/kg) in rice tops collected from Casiguran (Sorsogon), and Minalabac and Milaor (Camarines Sur). Such Zr levels can be due to the soils’ high clay and organic matter (OM) contents that promoted soil saturation by water. Index of bioaccumulation for Rb is 2.56, indicating that it can be easily taken up by rice plants. This study suggests that trace element concentrations in rice areas are controlled by soil properties and that Rb can be a potential toxic element in rice plants. Keywords - Soil science, rare trace elements, trace element sources, rice soils, Philippines