Philippine E-Journals

Concentrations of Rare Trace Elements in Major Irrigated Rice Areas of the Philippines

Jehru C. Magahud | Pearl B. Sanchez | Rodrigo B. Badayos

Discipline: Ecology

 

Abstract:

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 on 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.