Effects of Heavy Metals on Methane Production in Tropical Rice Soils

In a laboratory incubation study, the effect of select heavy metals on methane (CH4) production in three rice soils was investigated under flooded conditions. Heavy metals behaved differently in their effect on methanogenesis in different soils and methane-producing bacteria. Cd, Cu, and Pb inhibited CH4 production in all the soils. Zn stimulated CH4 production in the alluvial soil, but inhibited it in laterite and acid sulfate soils. Cr effectively inhibited CH4 production in the alluvial soil, but stimulated it in laterite and acid sulfate soils. The stimulatory effect of Zn and the inhibitory effect of Cr on methanogenesis in alluvial soil were attributed to their stimulation or inhibition of methanogenic bacterial population.