Mobility of Heavy Metals Present in Industrial and Municipal Sludge and Their Phytotoxicity Assessment during Early Seedling Growth of Kenaf (Hibiscus cannabinus)

Abstract

Agriculture is one of the prime components of economic development. However, enormous practices and deliberate ignorance have caused loss of fertility in agriculture soil. Industrial/municipal sludge being rich in soil nutrients attracts farmer for its application in agriculture land to support the crop productivity without knowing its adverse effects. Heavy metals are predominantly found in various sludge and they cause toxicity to the plants. Evaluation of phytotoxicity potential of heavy metals present in sludge is critical parameter in determining its land application and associated health hazards. Toxicity of metals depends not only on the total metal concentration but primarily on their availability in water soluble or bioavailable forms. This investigation is carried out to determine the heavy metal toxicity following Toxicity Characteristics Leaching Procedure (TCLP), bioavailability and extractability of heavy metal present in municipal and tannery sludge following the Community Bureau of Reference (BCR) sequential extraction procedure. Results revealed that chromium (Cr) (6209.6) was easily leachable followed by lead (Pb) (24.8), copper (Cu) (7.66), nickel (Ni) (5.46), cadmium (Cd) (3.71) in tannery sludge; whereas, the pattern of leaching was found to be Cr (1.58) > Cu (1.05) > Ni (0.14) > Cd (0.11) > Pb (0.09) mg L-1 in municipal sludge on application of TCLP. Sequential extraction revealed the presence of metals in exchangeable, reducible, oxydizable and residual fraction at varying degrees. Recovery of metals was found to be 65-98% in various phases. Phytotoxicity studies of sludge extracts on kenaf (Hibiscus cannabinus) revealed that the germination ranged between 75 to 95%, relative seed germination between 81.6 to 104%, relative root growth between 87.1 to 112% and germination index between 95 to 110%. It was found that sludge extracts have not caused adverse effects on seed germination and early seedling growth. Findings give direction for the eco-friendly and cost-effective management of municipal/industrial sludge. However, field trails need to be done before making land application plan.