Sorption behaviour of maneb in the agriculture soils and its correlation with soil properties
Abstract
Maneb is a broad spectrum fungicide, often reported as a carcinogenic, teratogenic and neurodegenerative agent. Thus, the occurrence of maneb at non-targeted sites is a cause of concern. The present study investigates adsorption– desorption behaviour of maneb in the agricultural soils to know its fate, mobility and availability in the soil. The sorption study was carried out by batch equilibration procedure. Maneb adsorption followed Langmuir isotherm and was accompanied by increase in manganese content of the soil. Maximum adsorption was observed in soil having the highest clay content. High maneb retention was observed in presence of soils modified with organic matter. The results of this study indicate that the clay and organic matter content of soil have significant influence on sorption behaviour of maneb. Amending soil with organic matter can reduce maneb pollution at non-targeted sites.
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Introduction
Maneb is a polymeric complex of manganese (Mn) with the ethylene bis (dithiocarbamate). Maneb, is a broad spectrum fungicide that is extensively applied against a wide range of fungal pathogens affecting ornamental plants, food and feed crops (Garcinuno et al., 2004). For instance, in the early years of this century in the USA approximately 2.5 million pounds of maneb are used annually targeting fungal diseases of almonds, apple, banana, bean, lettuce, walnut and peppers (US EPA,2005). In India maneb is abundantly used in states like Punjab, Haryana, Uttar Pradesh, Himachal Pradesh, Jammu and Kashmir, Tamil Nadu, Madhya Pradesh, Bihar and Andhra Pradesh for protecting food/feed crops (Bhushan et al., 2013). The problem related the difficulty in applying them to the targets and limiting their distribution in the non-targeted environmental sites. The extensive use of maneb has been shown to cause soil and water pollution in a banana production region of tropical Mexico (Geissen et al., 2010).
Maneb and its degradation intermediates have been reported to act as carcinogenic, neurodegenerative agent and teratogenic agents (Sharma et al., 2005; Baltazar et al., 2014). Baltazar et al., (2014) highlighted maneb as one of the potential etiological factor for neurodegenerative diseases like Parkinson disease, Alzhmeir’s disease and amyotrophic lateral sclerosis. Consequently, maneb was among the highest ranked hazardous pesticide for overall chronic health risk, while ranking the agriculture pesticides used in Yuma County, Arizona, USA (Sugeng et al., 2013). Sugeng et al., (2013) highlighted maneb as an endocrine disrupting carcinogenic fungicide.
Extensive uses at higher doses and hazardous nature of maneb have made it a global concern for policymakers and environmentalists (Bhushan et al., 2013). Its ecotoxicological impact, environmental mobility and rate of degradation in environment is influenced by its soil sorption behavior and physico-chemical properties of soil. Fungicide sorption and desorption in soil generally occurs at mineral, organo-mineral and organic particle surfaces. Since, soil has a complex composition and architecture, the overall sorption of a chemical is a composite of many surface interactions occurring in parallel (Wu and Gshwend, 1986). Better understanding of sorption and factors affecting it make it possible to regulate a pesticide’s uses and thus manage its environmental impacts.
The aim of the present study was to determine the adsorption-desorption behavior of maneb in the agricultural soils collected from Punjab and Himachal Pradesh, India. Kinetics and isotherm adsorption experiments were carried out to have a better insight into the sorption process of maneb in relation to the soil properties. Farmers tend to add organic matter (OM) to soil for increasing the yield. Hence, the influence of externally added OM on adsorption-desorption behavior of maneb was also studied.
Conclusion
This study contributes to the understanding of maneb sorption process in the agricultural soil. Clay content of the soil has significant influence on the adsorption of maneb only when organic content is low. Addition of OM to soil increased retention of maneb. The study suggests that use of organic matter in the agricultural fields restricts the mobility of maneb and prevents its pollution to non target sites. The results from the present study would help in designing of effective maneb management strategies in agricultural fields.