1874: First synthesized (does not occur naturally -- produced by the reaction of chloral (CCl3CHO) with chlorobenzene (C6H5Cl) in the presence of the catalyst, sulfuric acid)
Insecticidal properties used to control malaria and typhus (yellow fever) among civilians and troops in WWII in 1939
1948: high efficiency as a contact poison against several arthropods
After the war: agricultural insecticide (control potato beetles, coddling moth, corn earworm, cotton bollworm and tobacco budworms, etc) with mass production ( once as high as 220 million pounds of DDT a year )
1962: Environmental movement against DDT initiated by a book, Silent Spring, by American biologist Rachel Carson on the indiscriminate spraying of DDT in the US, questioned the logic of releasing large amounts of chemicals into the environment and on DDT harm to humans, cancer-causing , and a threat to wildlife.
June 1972: Large public outcry leading toUS EPA to ban the use of DDT on crops in US. This ban was a major factor for the comeback of the almost extinct bald eagle in US, the national bird of the United States.
Subsequently DDT was banned for agricultural use worldwide under the Stockholm Convention, but its limited use in disease vector control is still controversial today. Some say without using DDT there would be more damage n losses.
Method 1 (founded in 2004): Seaweed
Seaweed is a good source of sodium ions and DOC.
Sodium ions increase the DOC levels in soils as well as disperse the clay soil particles that bind DDT, thus making DDT more available for bioremediation
Increasing dissolved organic carbon (DOC) in the soil can increase the bioavailability of DDT for degradation by microbes as the microbe growth and metabolism is enhanced.
Illustration:
It is as though soil is sealed in an impenetrable box. DDT gets into this 'box' so the microbes that would normally break it down can't get at it. Seaweed has sodium in it. Sodium opens that box. It separates the tightly bound matrix that holds soil particles together and allows microbes to get in.
We could use any green waste, like grass clippings, as a source of dissolved carbon, we would have to add sodium to unlock the contaminants and the microbes. However, seaweed already contains both of these components.
However, seaweed also contains Nitrogen (a limiting nutrient for bacteria growth) and humic acid (has been shown to decrease the biodegradation rate of DDT). Thus, too high levels of seaweed addition can actually inhibit DDT degradation
Steps:
Flood the DDT contaminated soil to create anaerobic conditions so that DDD (metabolite of DDT) is formed which is much less persistent than DDT.
Research has shown that the initial breakdown of DDT into a breakdown product (DDD) depends on particular microbes that function best anaerobically (without oxygen).
Note: Should not create aerobic conditions because microbes under aerobic conditions lead to the formation of DDE, a more persistent compound than DDT.
Dry the seaweed under the sun and crush it mechanically to make the seaweed powder.
Scatter seaweed powder over contaminated soil and mix the soil using agricultural equipment to get maximum contact.
Results: Most effective mix is where 0.5% of seaweed powder can clean 80% of DDT in 6 weeks.
Method 2 (found in June 2010): Wax Strain
Microbial degradation using a bacterium Pseudoxanthomonas sp. Wax (from oil-contaminated site) to degrade DDT and simultaneously co-metabolize DDD, DDE and other organochlorine compounds from both sterile and non-sterile soils
The wax strain had the highest degradation efficiency among all of the documented DDT-degrading bacteria.
Optimum conditions:
Temperatures: 20 ºC to 37ºC
pH: 7 to 9
This method is done ex-situ (requires pumping of the groundwater or excavation of contaminated soil prior to remediation treatments.)
Steps:
Dig up 1cm to 20cm of soil
Isolate wax strain and inoculate the wax cells at 108 CFU g-1 soil. CFU = Colony Forming Unit
Autoclave at 121ºC for 15 minutes
Adjust moisture to 40% (wt/wt)
Incubate samples in the dark to preclude photolysis reactions. Photolysis reaction is a chemical process by which molecules are broken down into smaller units through the absorption of light.
Results:
20 mg/kg of DDT removed in 20 days
95% of DDT removed at 20mg/l in 72 hours
Due to broad substrate specificity, a strong degradation ability and adaptability to temperature variation, the wax strain is a promising candidate for the bioremediation of DDT-contaminated sites
High removal efficiency of DDT in non-sterile soil showed that the wax strain is potentially useful for the bioremediation of DDT-contaminated soil, even though there was competition between the indigenous populations and the inoculated strain.
Method 3: DARAMEND
It is a amendment-enhanced bioremediation technology for the treatment of POPs (Persistent Organic Pollutants) that involves the creation of sequential anoxic and oxic conditions à create suitable conditions for the various byproducts and enzymes of the microbes.
Steps:
Addition of solid phase DARAMEND® organic soil (where it contains naturally occurring consortium of microbes) amendment of specific particle size distribution and nutrient profile, zero valent iron, and water to produce anoxic conditions. This is then left undisturbed for 1 to 2 weeks.
These stimulates the biological depletion of oxygen generating strong reducing (anoxic) conditions within the soil matrix. à depletion of oxygen creates a very low redox potential, which promotes dechlorination of organochlorine compounds.
A cover may be used to control the moisture content, increase the temperature of the soil matrix and eliminate run-on/ run off
Dechlorination products will be formed in the process.
Periodic tilling of the soil to promote oxic conditions.
periodic tilling of the soil increases diffusion of oxygen to microsites and distribution of irrigation water in the soil.
Dechlorination products are subsequently removed and initiated by the passive air drying and tilling of the soil to promote aerobic conditions
The primary wastes generated are debris, stone, and construction material that are removed in the pretreatment process.
Repetition of the anoxic-oxic cycle until the desired cleanup goals are achieved.
The amount of DARAMEND® added in the second and subsequent treatment cycles is generally less than the amount added during the first cycle.
The duration of the treatment cycle is based on soil chemistry, concentration of contaminants of concern and soil temperature
Note: Soil moisture is maintained within a specific range below its water holding capacity. Maintenance of soil moisture content within a specified range facilitates rapid growth of an active microbial population and prevents the generation of leachate.
Design factor is the amount and type of soil amendments required for bioremediation. This is dependent on site conditions and the physical (textural variation, percent organic matter, and moisture content) and chemical (soil pH, macro and micronutrients, metals, concentration and nature of contaminants of concern) properties of the target soil.
These steps can be implemented in land farms in-situ or ex-situ: (Both treatment are 2 feet deep)
In situ:
the soil may be screened to a depth of 2-ft using equipment such as subsurface combs and agricultural rock pickers.
Can apply for more than 2 feet if use alternative soil mixing equipment or injection techniques
Ex-situ:
Contaminated soil is excavated and sometimes mechanically screened in order to remove debris
The screened soil is transported to the treatment unit
Limitations:
may become technically or economically infeasible when treating soils with excessively high contaminant concentration
requires a source of water (either city, surface, or subsurface).
cannot be applied to sites that are prone to seasonal flooding or have a water table that fluctuates to within 3-ft of the site surface à difficult to maintain the appropriate range of soil moisture required for effective bioremediation, and may redistribute contamination across the site.
Presence of other toxic compounds (heavy metals) may be detrimental to soil microbes
Soils with high humic content may slow down the cleanup through increased organic adsorption and oxygen demand.
Method 4: Vegetables
zucchini, tall fescue, alfalfa, rye grass and pumpkin as phytoremediators, growing them from seed on soil
All five plants removed DDT/DDE/DDT from the soil, but the best were clearly zucchini and pumpkin, both members of the Cucurbita family.
Their success was attributed to a high transpiration volume that induced a larger movement of plant sap, large above-ground biomass and the particular composition of the root exudates.
Method 5: Xenorem
combines organic compounds derived from wood pulp, straw and animal manure to rapidly and naturally break down chlorinated pesticides, such as DDT, from contaminated soils.
Monitor temperature and oxygen levels is important
Method 6: Other cultures
In 1977: Certain cell suspension cultures of Petroselinium hortense and Glycine max
In 2005: Hairy root cultures (Cichorium intybus) are promising in the degradation of DDT
Case Study: DARAMEND, Montgomery (Alabama)
Bioremediation of pesticides contaminated Agriculture and Nutrition (THAN) Superfund Site, Montgomery, Alabama.
located on the west side of Montgomery, Alabama, about 2 miles south of the Alabama River
16 acres in area
Previous site operations involved the formulation, packing and distribution of pesticides, herbicides, and other industrial/waste treatment chemicals
contaminated soil and excavated sediments (approximately 4,500 tons)
September 28, 1998, start treatment
Steps: Divided to 12 zones
Daramend and iron
Water holding capacity
Matrix moisture content:
90% of soil holding capacity
pH: 6.6 to 8.5
Add hydrated lime: 1,000 mg/kg (3rd, 6th, 12th cycle)
4. Irrigation (Anoxic: 7 days)
5. Soil tilted daily (Oxic : 4 days)
6. Repeat steps 1, 4 and 5 for 15 cycles
Results:
As seen, the efficiency of this method is rather high as we compare the initial and final concentrations of DDT, DDD and DDE.
Efficiency:
This method has proven to be economical and has a short duration. Thus, with such high efficiency and affordable cost, this environmentally friendly method is suitable to be used for large scale projects.
DDT is very harmful and the contamination will still continue today thus is it important to find a way to treat in. Future research is needed for the bioremediation of DDT. The methods we have reviewed are discovered in recent year hence it is not applied commercially as it is still under experimental stage therefore we have limited case study.
In our opinion, there will be a rise in this area of research.
