Investigating chitosan interaction with lead on enzyme activities in two acidic and calcareous soils

Chitosan is a natural and destructive polymer that consists of glucosamine units, which, due to reactive groups, can reduce the availability of heavy metals and change soil enzyme activities which is an indicator of soil quality. However, little information is available on simultaneous effect of chitosan and heavy metals on soil enzymes activities. In this study, the interaction of chitosan at three levels of control, low molecular weight (LMC), and high molecular weight (HMC) with Pb at three levels of 0, 50 and 500 mg/kg on available soil lead (Pb) investigated on activity of acid and alkaline phosphatase, L-glutaminase and fluorcine diacetate hydrolysis enzymes in two different soils, Lavark and Langroud. The results were statistically compared. Both chitosan types significantly reduced available Pb concentration in two soils, but HMC was more effective. In Lavark soil, LMC and HMC application to Pb treatments significantly increased the activity of acid and alkaline phosphatase, L-glutaminease and fluorcine diacetate hydrolysis compared to control treatments. In Langroud soil, LMC application to Pb treatments significantly increased L-glutaminease activity, but did not affect the activity of other enzymes. The HMC application in Langroud soil also did not significantly affect activity of any enzymes compared to control. Level of 50 mg/kg Pb in the presence of chitosan significantly decreased acid phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate hydrolysis in Langroud soil compared to control, but had a positive effect on the activity of other enzymes. Level of 500 mg/kg Pb in the presence of chitosan also reduced acid and alkaline phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate in Langroud soil, but significantly increased the activity of other enzymes. Generally, increasing or decreasing enzyme activity due to the simultaneous presence of chitosan and Pb depended on soil, enzyme, Pb concentration, and chitosan type.