DDT is a white, solid, crystalline powder with no taste or odor. DDT (C14H9C15) is derived from reaction between chloral and chlorobenzene in presence of fumes of sulfuric acid. DDT is insoluble in water and it is soluble in organic solvents such as, fats and oils. DDT (dichlorodiphenyltrichloroethane) is an organochlorine pesticide widely used to control mosquito and insects that carry diseases like malaria, typhus, and other harmful diseases and pest in agriculture (Martin, 2008; Raghavendra et al., 2010). DDT was banned in the U.S. in 1972 because it was identified to cause damage in birds and other wildlife, but it is still used in some developing countries (Bhuiyan et al., 2008). It is still present in environment due to current use in other countries. DDT and its breakdown products (DDE and DDD) can easily break down by sunlight, but they are very hard to dissolve in soil. DDE (dichlorodiphenyldichloroethylene) and DDD (dichlorodiphenyldichloroethane) are two major metabolites and breakdown products of DDT. DDD was also known as pesticide, but it was banned whereas DDE does not have any commercial use (Eskenazi et al., 2009).
DDT was first synthesized in 1874 by Othmar Zeidler. In 1940, DDT was first used to treat Dutch elm disease. DDT was majorly used in World War II to protect troop and civilians from diseases. In 1939, Paul Mueller discovered DDT as insecticide and he won the Nobel Prize in 1948 for it. After this, people started using DDT as pesticide for their home, agriculture purpose and in gardens (Eskenazi et al., 2008). However, DDT started to cause diseases during this time and this increases public concern to Rachel Carsonâ€™s Silent Spring. Rachel Carsonâ€™s Silent Spring was published in 1962, which contains environmental impacts of DDT in the US (ATSDR, 2002; Eskenazi et al., 2008; Martin, 2008).
DDT is strongly absorbed by soil and remains there for long period of time (Bhuiyan et al., 2008). They released from soil by various types of reactions such as, runoff, photolysis, aerobic and anaerobic biodegradation and volatilization (van den Berg, 2009). In surface water, DDT will bind to particles that are present in the water and sediments. DDT is taken up by small organisms and fish from the water and then bioaccumulate in organisms to higher trophic levels. DDT deposited into the adipose tissues and fats in organisms. DDT shows bioaccumulation and biomagnification as it has lypophilic property (Bhuiyan et al., 2008). In 1950s, first evidence of DDT toxicity in bald eagles, robins, osprey, pelicans, peregrine falcon, and fish-eating mammals was observed (Xiao et al., 2008; DDT: An Introduction, 1996; Martin, 2008).
This paper has five objectives: (1) To discuss the sources and main causes of DDT; (2) To discuss its mechanism of action as insecticide or pesticide; (3) To discuss the health problems and toxicological effects associated with DDT; (4) To discuss the environmental impacts of DDT; (5) To discuss control measures and various methods of dealing with DDT sources and problems.
DDT in the Environment
DDT is not soluble in water but it can form strong bonding with soil particles. DDT is still present in environment in soils that were exposed to DDT during earlier time. DDT is a volatile so it can be transported and evaporated as a gas. DDT is not commonly found in groundwater because it is less soluble in water and it will more likely to bound with soil particles rather than water molecule (ATSDR, 2002; Walker, M., Powell, P., 2003; van den Berg, 2009).
DDT can be present in air in the form of gas or it form small aggregation with dust particles. The chemical evaporate in warm temperature and it can travel long distance as a gas from the site of application. Such as, the study was conducted in Medford, Oregon where, it has climate cooler and soil is full of organic matters. It showed only 17 to 18% evaporation of DDT from the soil during five years of time period. The similar study was conducted at Arizona showed that DDT showed its presence in the air after six months of application. It showed up to 50% of DDT evaporated out from the soil within 5 month of period of time (van den Berg, 2009; Walker, M., Powell, P., 2003). In the form of vapor, DDT has 2 days of half-life time period (ATSDR, 2002). In tropical soil, DDT has half life within the range of 3 to 7 months while it is up to 15 years in temperate soil. DDT has half life time in human is of greater than 4 years (van den Berg, 2009).
DDT and DDE are low soluble in water so they generally concentrated in the top region of soil. In soil, many bacteria degrade DDT and then they converted it into DDE, which is less toxic but more persistent in the environment (Walker, M., Powell, P., 2003).
Mechanism of Action of DDT as Pesticide
DDT generally affects nervous system of insects. It affects in neuron and opens sodium channels, which make them to cause fire rapidly. This condition leads to spasms and then death (van den Berg, 2009).
Sources of DDT
DDT is a synthetic organochlorine pesticide. Many pesticide companies have been involved with DDT production. By 1991, only Hindustan Insecticides, India; Enichem Synthesis, Italy; and P.T Montrose Pesticido Nusantara, Indonesia were listed as basic producers by UN Environment Program (UNEP). It was also produced in Mexico. There is no production record found for DDT worldwide (van den Berg, 2009; DDT Factsheet, 1998).
DDT is entering into environment through various natural and anthropogenic sources. There are some anthropogenic sources that are caused by human. Many studies conducted on anthropogenic sources because they can be easily controlled and eliminated to reduce the DDT concentrations from the environment. There are many reasons behind the presence of DDT residue in environment, such as manufacturing and application of DDT to control tropical diseases like malaria, transport of DDT by air, DDT production continues by using other names like Dicofol, and dumping of waste where the DDT is totally absent. These are some sources of DDT which are anthropogenic (Dymkowska-Malesa, 2009).
The major source of DDT entering in water bodies is agriculture run-off from fields that were earlier sprayed with DDT to control insects or pests from that area. Soils accumulate DDT from direct application of DDT in to that particular soil as pest control. Runoff from heavy rains can wash deposited DDT with soil particles and sediments directly into nearby water body, which allows DDT to enter the aquatic food chain. DDT is lypophilic compound so it can easily get deposited into body fat or adipose tissues of aquatic animals and then DDT shows bioaccumulation and further biomagnification (van den Berg, 2009).
Many lakes and streams were directly sprayed by DDT using aerial spraying of crops. DDT cannot contaminate ground water as it strongly binds with soil particles. Industrial waste and effluent from pesticide industries may also contaminate aquatic environment by DDT. Leaking landfill sites, historical uses, long distance transportation through atmosphere as a gas and illegal use of old stock are examples of sources of DDT that contaminate aquatic environment as well as atmosphere by adding DDT (Dymkowska-Malesa, 2009).
DDT can deposit in plant tissues as well as in the fatty tissues of animals, birds and fish. DDT can enter into the body by three common routes such as, inhalation, ingestion and dermal exposure. Most common route of exposure to DDT is ingestion of contaminated food. It can enter into the body by inhalation and by skin but it is rare (Dymkowska- Malesa et al., 2009; Schecter et al., 2010; Sereda et al., 2009).
Health Problems and Toxicological Effects Associated with DDT
Humans are exposed to DDT from contaminated foods, such as leafy and root vegetables, fish, poultry, fatty meat, etc. Some countries still use DDT as pesticide, so eating foods which are imported from other countries that allow the use of DDT exposed people to DDT. Drinking contaminated water or breathing contaminated air or soil particles near waste sites, industrial areas or landfills also increase the chances of getting exposed with DDT (ATSDR, 2002; Dymkowska-Malesa, 2009; Schecter et al., 2010; Sereda et al., 2009).
DDT is an environmental health issue largely because of its lypophilic property which makes it enable to store in fatty tissues of organisms and another property is biomagnification (Tomza-Marciniak, A., Witczak, A., 2009). DDT, DDE and DDD can be measured in blood, tissue, fat, urine, breast milk (Turusov et al., 2002) and semen. These are some body fluids, that shows the presence of DDT and it can only predict the chances of health effects in the person. When DDT enters into human body, it deposited into fatty tissues, adipose tissues (Ociepa-Zawal et al., 2010), and organs such as testes, thyroid, adrenal, etc. It shows deposition in liver and kidney like major organs, too (Sereda et al., 2009; van den Berg, 2009).
There are two types of toxicological effects associated with DDT: (1) Acute toxicity: DDT is slightly toxic to mammals through oral route of absorption. LD50 values of DDT exposure through oral route are different in different animals such as, in rats it is range from 113 to 800 mg/kg; 400mg/kg in rabbit; 300 mg/kg in guinea pig; 500 to 750 mg/kg in dogs and more than 1,000 mg/kg in goats and sheep. When DDT enters through oral route, it increases absorption into the areas of high fats in gastrointestinal tract. DDT is generally not toxic via dermal route of exposure. Acute effects of DDT on human shows symptoms like nausea, diarrhea, irritation of eyes, nose, and throat, increase liver enzyme activity, excitability, malaise, etc. and upon higher doses, it shows symptoms like tremors and convulsions (EXTOXNET PIP, 1996). (2) Chronic toxicity: DDT cause chronic effects on the major organ systems of the body. It affects nervous system, liver, kidney, and immune system. Immunological effects by DDT shows reduce antibody formation (EXTOXNET PIP, 1996; ATSDR, 1994; Eskenazi et al., 2009; Sonkong et al., 2008).
DDT causes reproductive effects in laboratory animals. Oral dose of 7.5 mg/kg/day for 36 days in rats resulted in sterility. In rabbits during periods of gestation, doses of 1 mg/kg/day resulted in decreased fetal weights on 4-7 days and 10 mg/kg/day resulted in resorptions on 7-9 days. Dose of 1.67 mg/kg/day in mice resulted in decreases embryo implantation (ATSDR, 1994; Eskenazi et al., 2009). DDT is also known as endocrine disruptors. DDT is a synthetic organochlorine pesticide that when entered into the body either blocks or mimics hormone systems and disrupts the normal body functions. Many studies indicate that DDT has estrogenic effects in mice, in which DDT increased the weight of uterus in mice that is called as uterotropic effect and development of pseudo estrus in rats also caused by DDT. DDT causes permanent, male-to-female sex reversal upon a single exposure of eggs toÂ o,pÂ´-DDT in medaka fish. In rats, DDT can facilitate implantation, maintained pregnancy and it can exert an uterotropic effect, too (Turusov et al., 2002; Eskenazi et al., 2009).
DDT and DDE can easily cross the placental barrier to transfer from mother to fetus; therefore it can cause harmful effects to fetus (Sapbamrer et al., 2008). DDT can causes teratogenic effects in fetus or it can cause premature birth in pregnant women. Maternal dose of 26 mg/kg/day in mice during the period of gestation to lactation resulted in impaired learning performance in maze tests (ATSDR, 1994; Eskenazi et al., 2009; Lea et al., 2008; Sapbamrer et al., 2008). Health effects of DDT also include pregnancy loss during first few months, leukemia, diabetes, loss of fertility, cancer like pancreatic, liver, breast (Cohn et al., 2007; Ociepa-Zawal et al., 2010), testicular (Cohn et al., 2010), and other cancers (Turusov et al., 2002; Eskenazi et al., 2009), and neurodevelopmental deficiencies (van den Berg, 2009; Beard, 2006; Cox et al., 2007).
Many studies show mutagenic effects of DDT by using in vitro and in vivo genotoxicity assays which shows chromosomal aberrations. People who directly or indirectly exposed to DDT showed higher number of chromosomal damage in their DNA. This shows that DDT causes genotoxic effects in humans. It also shows organ toxicity in major organs of human body, such as liver, kidney, nervous system (ATSDR, 1994; Eskenazi et al., 2009; EXTOXNET PIP, 1996).
The immune system has shown signs and symptoms of sensitivity to DDT. There is no known data on effects of DDT on function of immune system of humans. However, some animal studies have indicated that DDT effects immune cell ratio, development of immune response, cellular response and also antibody production (Eskenazi et al., 2009).
Environmental Problems Associated with DDT
DDT can also cause problems for wildlife, especially birds, fish, etc. DDT enters into the aquatic environment via natural and anthropogenic sources; it takes up by some small fish or other aquatic animals. DDT is lypophilic compound so it deposited in the fatty tissues of fish or other organisms. DDT may bioaccumulate significantly in fish and other aquatic species, and it also shows biomagnification. A rainbow trout shows 160 days of half-time for elimination of DDT. Bioaccumulation occurs with very little amount of DDT concentration in fish and other aquatic species. Predatory birds or large fish feeds on them and resulted in exposure to DDT (Xiao, 2008; Tomza-Marciniak, A., Witczak, A., 2009). Many studies showed that DDT and DDE can act as carcinogenic, neurotoxic, immunotoxic and reproductive effects on animals (Turusov et al., 2002).
In birds, exposure to DDT mainly occurs through food chain and sometime the direct exposure to eggs or birds also observed. In 1950s, first evidence of DDT toxicity was observed in bald eagles, robins, osprey, pelicans, peregrine falcons and other fish eating mammals. In birds, DDT and DDE reduce Ca-dependent ATPase activity in the shell gland of birds resulting in shell thinning and increased egg damage during incubation period (Turusov et al., 2002).
It is easy to control anthropogenic sources of DDT than natural sources. DDT can be removed by many chemical and biological processes. Once it gets into the food chain, recovery becomes difficult as it shows bioaccumulation and biomagnification.
Many organochlorine compounds or pesticides are degraded by microorganisms. Microbes possess enzyme system to degrade organochlorine pesticides, such as dehydrochlorination, isomerization, oxidation, etc. Microbial degradation of DDT is observed by two ways; aerobic and anaerobic degradation. Many studies reported that bacteria like Serratia marcescens, Alcaligenes eutrophus A5, Lactobacillus plantarum, Micrococcus varians, and Pseudomonas sp. can degrade DDT by the process of aerobic degradation. One study reported that Fungus named white rot fungi can do mineralization of DDT (Sonkong et al., 2008). Degradation and transformation of DDT using microorganisms will provide most proficient way to deal with the problem, which is bioremediation.
Boussahel et al., 2009 studied adsorption and kinetic process to remove DDT from aqueous solutions using low-cost adsorbents. During the study they used batch adsorption technique to determine adsorption efficiency using two types of adsorbents, wood sawdust and cork wastes. The result of the study was compared with a commercial powdered activated carbon. Langmuir isotherm was used to calculate the adsorption capacity. The study showed that wood sawdust is the most effective type of adsorbent for the removal of DDT from aqueous solutions. It can be used in decontamination of water and also in treatments of waste water in agriculture purpose and industries.
DDT is a toxic compound that exhibits bioaccumulation and biomagnification through food chains. After World War II, DDT started causing problems in human health and in 1950s, DDT cause detrimental effect on birds. These are some events that showed the dangers of DDT for human as well as for environment. Many studies over the years have produced considerable amounts of evidence to prove the toxic effects of DDT. DDT was banned in U.S. very long ago but some other countries still using DDT as pesticide to prevent malaria. Methods and solutions were found, that replaces DDT to control malaria. Many chemical and remediation processes was found that totally remove DDT from solid and aqueous solutions but still have much room for improvement. Due to biomagnification, the effect of small amounts of DDT will be felt many years into future. It has been so long that U.S. banned on DDT but still the outbreak of birds problems and human health problems going on.
Future Research Needs
Several methods found for detection of DDT including enzyme immunoassay have been developed (Hirano et al., 2008). One of the major problems with DDT is biomagnification. There are so many methods like volatilization, bioremediations, and adsorptions procedures currently being studied (Sonkong et al., 2008; Boussahel et al., 2009). DDT in soils and sediments form strong bond so it is very hard to remove DDT from soil and it cannot degrade easily in soil. Methods found for the removal of DDT from aqueous solutions (Boussahel et al., 2009). Presence of DDT in organisms like birds, fish, etc is the area of concern in future that needs to be reduced. Much future research is needed to introduce new chemical compound that can deal with malaria like diseases and is comparatively less toxic to human and environment.
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