Cycle of heavy metals in the soil of livestock farms in an acidic zone of the central region of Thailand

The purpose of the present study was to examine the connections between heavy metal concentrations in the soil, pasture grass, and livestock manure on farms located in an acidic soil zone of central Thailand. Samples of the soil, grass, and livestock manure were collected from three farms, and were tested for Cd, Pb, As, and Hg. Multiple indicators were employed to assess the pollution levels of the farm soils. The results showed that the amounts of heavy metals in the soil were in the order Pb > Hg > Cd > As; in grass the order was Pb > As > Cd > Hg, and in livestock manure this was Pb > As > Hg > Cd. The soil pH level influenced the quantities of Hg and Ag in the soil. Concerning individual indicators, Igeo and CF indices showed that Hg was present at high levels in farm soils, but an integrated indicator PLI was less than 1, suggesting that soil in the farms was not significantly contaminated, in contrast to the individual indicators. Heavy metal accumulation depended on the species of grass, and the element content in manure was higher than in grass used for feeding the animals, including supplements given to animals by farmers. However, the levels of Cd in the livestock farms demonstrated a relationship among soil, grass, and manure. The heavy metals in manure from animal farms were below the thresholds at which they could be utilized as a soil amendments for organic farming or for safe food production. However, the heavy metals in the farm soil could possibly be dispersed to other locations.