Effect of o-phenylenediamine on Cu adsorption and desorption in red soil and its uptake by paddy rice ( Oryza sativa)

Abstract

A study was carried out of Cu adsorption and desorption processes in red soil as affected by o-phenylenediamine ( o-PD) in the range 0–80 mg/l. The results indicated that the presence of o-PD enhanced Cu adsorption in red soil in weakly acid media, meanwhile, desorption percentage of Cu from soil, extracted by 1.0 M MgCl 2, also increased when Cu adsorption in soil occurred in the presence of o-PD. The response of paddy rice to Cu in red soil shows that Cu toxicity was mitigated in the presence of o-PD and that the Cu concentration in rice straw decreased with increasing concentration of o-PD from 0 to 4.0 mmol/kg in soil. The fractions of background Cu in soil did not change noticeably in the presence of o-PD, whereas the effect of o-PD on the fractions of added Cu was significant. It was found that the exchangeable and carbonate bound Cu fractions decreased and the fraction of Cu bound to Fe–Mn oxides and organic matter increased with increasing o-PD concentration in soil when Cu was added at the same rate. Copper concentration in rice straw was significantly correlated with exchangeable Cu ( r=0.961) and carbonate bound Cu ( r=0.959) in soil. This result implicates that the behavior of Cu in soil is likely to be affected by organic pollutants containing amino groups.