By: Gomal Amin
What is Endosulfan?
Endosulfan is a neurotoxic
organochlorine insecticide, which is used worldwide for pest control and its
residues have been remained for long periods in soil, water bodies and agricultural products. Endosulfan is highly insoluble in water. Hence, mostly it
will be associated with soil. It is reported that, the half-life of soil bound
Endosulfan was much higher than that of aqueous forms. Health and environmental
concerns have led to an interest in detoxification
of endosulfan in the environment.
Effect on Human Body:
High doses of endosulfan in
humans primarily affect the central nervous system, resulting in respiratory
depression, dry mouth, convulsions, and possibly death. Low doses have been
shown to compromise the immune system, liver, kidneys and reproductive system
in animals.
How it enters to Environment:
Endosulfan was used as potential
pesticide, after its application on plants it will attach with soil particles
and soil erosion, run-off, spray drift, and atmospheric deposition contribute
to releases of endosulfan to aquatic ecosystems.
Degradation products:
Endosulfan diol, Endosulfan
sulfate, Endosulfan ether, and Endosulfan lactone
How Experiment is conducted and its conditions:
·
The extent of biodegradation of endosulfan was 80%
in aqueous and 60% in soil slurry during 60 days in anaerobic conditions.
·
Pure as well as mixed microbial cultures
utilized ES as a carbon and sulfur source in both aqueous and soil mediums.
·
Methanogens
were identified in an anaerobic mixed culture degrading ES and the major
degradation product was endosulfan diol (ESD) along with traces of, endosulfan
sulfate, endosulfan ether, and endosulfan lactone
·
Study was done to obtain the kinetics of
complete biodegradation pathways of ES in the aerobic and anaerobic
environments, and identify the rate limiting steps so that the accumulations
and persistence of the toxic metabolites could also be predicted.
·
The 100 g L-1 of anaerobic seed soils were used
to inoculate the enrichment cultures in 200mL autoclaved basal nutrient media
NS2
·
The composition of NS2 (Basal nutrient media)
used to enrich anaerobic culture was (in mg L-1): KH2PO4 8300, K2HPO4 6800, NH4Cl
1300, MgSO4.7H2O 100, Fe2 (SO4)3 10, Na2 EDTA 15, Cu (NO3)2 1, ZnCl2 2.5, MnCl2
1, CoCl2 0.05, H3BO3 1, and Na2SO4 4. The pH of the solutions was adjusted to
7.
·
NS2was purged with nitrogen earlier to use. ES
at a concentration of 0.491 mM was prepared using market grade ES, was added as
a carbon source in anaerobic cultures. The culture was maintained at room temperature
(~25 C’). The regular media replenishment was done at an interval ~15 d for
anaerobic culture. After 6–8 cycles, the cultures were separated from media using
streak plate on NS2 base containing 1.5% Agar. Then the colonies were moved to
anaerobic environment.
·
After centrifugation and suspending in phosphorus buffer saline of neutral ph,
the inoculums of bacterial culture is proliferated in different plates
containing Anaerobic Agar.
·
The degradation products were extracted from
solution using Soxhlet Extraction
procedure (USEPA Method 3540).
·
Biodegradation
experiments in aqueous cultures:
The anaerobic biodegradation experiments were conducted for
60d, respectively, in 40 mL borosilicate glass vials, crimp sealed with Teflon
lined septa. In the aqueous phase experiments, each autoclaved vial contained
35 mL of 2.46l M of ES solution prepared in NS2 (anaerobic) media, and 1 mL of
either microbial seed in PBS or autoclaved phosphorus buffer saline. The vials
were placed on a rotary shaker at 20 rpm and kept at room temperature (~25 C’).
At pre-determined sampling times, vials in duplicate were removed from the
shaker, and samples were processed for extraction and analysis in GC–MS.
Pathway of degradation:
Hydrolysis to ESD was the only
route of ES degradation in anaerobic medium which was achieved using first
order kinetics model. The degradation pathway anaerobic degradation of ES was
based on the time of appearance, peak position and centre of mass of
concentration profiles of the metabolites.
In aqueous media, hydrolysis to
the less toxic endosulfan diol is expected to be the dominant transformation
pathway. For their potential degradation of endosulfan and its metabolites,
i.e., endosulfan sulfate, endosulfan ether, and endosulfan lactone, in
anaerobic condition.
Under anaerobic conditions, ES was
hydrolyzed to ESD which was converted to ESE. ESS and ESL were not detected
in the anaerobic system but according to some other experimental results the
ESS presence is due to lack of oxygen or anaerobic condition.
A new unknown metabolite is also
detected which is degradation product of ESE and/or ESL and is now known as ESU1.
Mass balance:
The carbon, chlorine and sulfur
balance computed from the concentrations of the parent compound and identified
metabolites showed that sulfur started to decrease in anaerobic aqueous
cultures without any lag. The release of sulfur show that it will serve as food
source for bacterial growth. On the other hand, no immediate loss of carbon and
chlorine were recorded in any medium and the total carbon and chlorine started to
decrease only after 15 d in anaerobic medium.
In the degradation pathways of ES
to ESE in the anaerobic environment, no carbon and chlorine is lost. Loss of
carbon and chlorine can only be attributed to further degradation of ESL or ESE
to smaller products. These are also the times when significant build-up of ESU1
started in these systems, indicating that ESU1 was a degradation product of
ESE/ESL.
Results:
Anaerobic mixed culture was able to
degrade ~82% of the total ES in 60 d
References:
Paper name: Kinetics of the biodegradation pathway of
endosulfan in the aerobic
and anaerobic
environments
Writers name: Manoj K. Tiwari,
Saumyen Guha
Journal name: Elsevier –Chemosphere
Publication: Chemosphere 93
(2013) page No 567–573
Journal homepage: www.elsevier.com/locate/chemosphere
0 comments:
Post a Comment