R. Janarthanan and A. Murugan*

Department of Microbiology, Periyar University, Salem – 636 011, Tamil Nadu, India.

Abstract

Pesticides are widely used to control the pest as well as to improve the yield of agricultural products. Pesticide applied in the soil affects the microorganisms, soil enzymes, and physicochemical parameters in the soil and in turn affect the soil fertility. Understanding the impact of pesticide on the soil both, short-term and long-term exposure would provide a set of analytical data for risk assessment and resilience of the soil parameters. This would open up other possible ways given to improve the crop productivity. This review mainly focuses on standard biomarkers such as microbial enzymes, soil enzymes novel proteins, and microbial community other parameters developed as indicators of pesticide contamination.

Keywords: environment health, pollutants, degradation, remediation, rhizosphere.

Introduction

Pesticides are anthropogenic products intended to control pest in the agriculture as well in the household maintenance. It been used since the end of the Second World War (EPA 2009) and has been reached to two million tons per year (De et al. 2014).  Pesticide usage in India is only 3.75 %, which is comparatively less than any other country in the global scenario. HCH, DDT and Malathion are commonly used pesticides (Brucker et al., 2008). Organophosphates and carbamates are the synthetic pyritheriod used commonly but extremely toxic to living forms (Van Wijngaarden et al. 2005). In India the maximum (44.5%) usage of the pesticide reported in cotton field (Agnihotri 1999). These insecticides effect on beneficial microbial diversity in the soil and decrease in soil fertility (Johnsen et al. 2001).

  1. Fate of Applied Pesticide

Applied Pesticides directly reach the soil through spray drift, run-off, or wash-off vectors (Racke et al. 1997). Pesticides transport to contaminate water, air, plants, food and ultimately into human via, runoff and subsurface drainage; interflow and leaching; and the transfer of mineral nutrients and pesticides from soils into the plants and animals that constitute the human food chain (Abrahams 2002). The pesticide that becomes to be as integrated into transport and degradation processes that characterize soi1 ecosystems (Glatfelter et al. 1989). The pesticides in the environment undergo volatilization, leaching, adsorption, photodecomposition, degradation by other non – biological processes and biodegradation (Sawhney et al. 1986). Biodegradation is the process that involves the use of living microorganisms to detoxify or degrade the pollutants into less toxic forms (Zhang et al. 2011). Several bacteria utilize pesticide as a carbon, energy source and convert into simple harmless forms.

 

  1. Impact of Pesticide on Soil Enzymes

Extracellular enzymes secreted around the microbial cells (Mayanglambam et al. 2005) influences soil fertility (Antonious 2003; Bucket and Dick 1998). Direct effect on the soil microbial community reflects reduced production of many extracellular enzymes responsible for biogeochemical cycles (Klose et al. 2006). Nevertheless, residual pesticides in the soil alter the functions of hydrolases, oxidoreductases, and dehydrogenase, phosphatase activities (Menon et al. 2005; Monkiedje and Spiteller 2002); (Kucharski et al. 2000; Trasar-Cepeda et al. 2000). Effect of pesticide on the bacteria, fungi and actinobacterial enzymes like dehydrogenase, phosphatase, and to their respiratory activities are detrimental. Pesticide like Monocrotophos and quinalphos (organophosphates), and cypermethrin (pyrethroid), tend to increase the activities of cellulase and amylase enzymes. Interestingly, combinations  involving monocrotophos with cypermethrin demonstrated synergistic and antagonistic effects on both enzymes in the soils activity of arylsulfatase (Table 1) and β-glycosidase implying that S-mineralization in soils and the total oxidative potential of microorganisms are affected by pesticides (Gundi et al. 2007).

  1. Impact of Pesticide on Soil Microbes

Applied pesticide can change the environment in the size and structure of microbial community. Pesticides which leads to a shift in the microbial community enhances the growth and establishment of species that are capable to degrade this type of chemical fertilizer, pesticide and change the overall soil quality (Table 2) and microbial community either short term and long term effects. Most of the farmers prefer to use chemical pesticide such as thiame thoxam, group of the neonicotinoids, pyrthroid are widely used, is resulting in chemical residue in soil. Residual pesticide in the soil disturbs the physical-chemical properties of soil that leads change in the soil fertility. Ultimately, the bacterial, which has the capacity to transform or degrade the pesticides, surpass the plant growth stimulating bacteria. They can metabolize even the most persistent pesticides either by the utilization of the compounds as sources of energy, or by co-metabolism with other substrates supporting microbial growth Bitmann et al. 2005; Ratcliff et al. 2006 and Dick et al. 2010).

  1. Impact of Pesticide on Soil Nutrients

The indiscriminate use of pesticide has found to alter soil biodiversity that contribute to soil fertility (Tilman et al. 2002). Chemical pesticides are toxic to soil microorganisms; hence, physiology in soil altered when particular populations are altered. Pesticide also affects the size of soil populations (Edwards et al. 1973). Most of the pesticides persist in the soil for such a long period to absorb by plants grown in a field year later (Anonymous 2009). Persistence of pesticide would influence soil population either by increasing the community, which can degrade pesticide. Hence, the loss of the population that is responsible for the release of many of the macro, micro, and trace elements in the soil disrupts the bio-geo cycles.

  1. Soil Enzymes as Indicators of Soil Fertility

Soil Enzymes are biological catabolism of soil organic and mineral components. Soil enzyme activities closely relate to soil organic matter (Table 3), soil physical properties and microbial biomass, changes much faster than other parameters, thus providing early indications of changes in soil fertility, and mostly involve simple procedures (Dick et al. 1996). In addition, the soil enzyme activities are measures for microbial activity, soil productivity, and inhibitor of pollutants (Tate 1995). Well-documented and quick assays are available for a large number of enzyme activities (Dick et al. 1996; Tabatabai 1994). These enzymes include dehydrogenase, glucosidases, urease, amidases, phosphatases, arylsulphatase, cellulases, and phenol oxidases.

 

Conclusion

Impact assessment due to the agricultural usage of pesticide would reveal the many changes taking place in the field. Such chances would be easy tools to evaluate the impact of applied pesticide on all forms, including soil microbes, plant, insects, and human. It will also address many other unresolved questions with regard to soil fertility, emergence of multi drug resistance, taro genic effects in many forms as well as premature puberty in women. Therefore, based on the above discussed data community can develop specific biomarkers for mutual exposure taking advantage of the ongoing characterization of toxicity signaling pathways and cause of many unknown diseases.

Acknowledgements

We thankful for financial support from UGC- BSR fellowship, New Delhi.

 

Conflict of Interest

Authors declare no conflict of interest

 

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Table 1 Impact of Different Pesticides on Soil Enzymes

Pesticides
 Enzyme
            Impact
References
Carbendazim and imazetapir

 

Nitrogenase
Pesticides reduced nitrogenase activity in R. leguminosarum, S. meliloti, and Bradyrhizobium sp. in pot and field conditions
Niewiadomska 2004
Metalaxyl

and Mefenoxam

Phosphatase
Decreased enzyme activity
Sukul 2006
Acetamiprid
Nitrate reductase
 arginine deaminase activities

 

Singh and Kumar, 2008

Table 2 Impact of different Pesticides on Soil Microflora

Pesticide
Microbial species
Effects
References
 

Methamidophos

 

 

Soil microflora

 

Decreased

 

 

Wang et al.(2007)

Atrazine

 

Chlamydomonas

Reinhardtii

Inhibited
Reboud et al. (2007)
Methamidophos

 

Soil microbes
Decreased
Wang et al.(2006)
Mefenoxam, metalaxyl
N – fixing bacteria
Inhibited
Monkiedje et al. (2002)

 

Carbendazim and imazetapir

 

Soil microorganisms
Reduced
Niewiadomska (2004)
Atrazine, isoproturon,

 

Bradyrhizobium sp.
Inhibited
Khan et al. (2006)

Table 3 Soil Enzymes influencing mineral cycle

Soil enzyme
Enzyme reaction
Mineral cycle
β-glucosidase
Hydrolysis of  Cellobiose
Carbon
Cellulase
hydrolysis of Cellulose
Carbon
Phenol oxidase
hydrolysis of Lignin
Carbon
Urease
hydrolysis of Urea
Nitrogen
Phosphatase
Release of PO4_
Phosphorous
Arylsulphatase

Urease

Protease

Release of SO4_

Hydrolysis of urea

Hydrolysis of protein

Sulfur

Nitrogen

Carbon