Types of Toxicology Data Used in Making the Decision
The type of toxicology data used in making such a decision is subject to the cumulative estimated dietary intake (CEDI) values. DDT does not have very high CEDI levels. For substances with such low CEDI values (between 0.5 and 50 ppb), two types of genotoxicity studies have been recommended. These tests are the mouse lymphoma assay (or vitro cytogenetic damage) and the bacterial mutagenicity assay.
Substances entering the body at such low levels usually present little challenge in and of themselves (Van Den Berg, 2009). According to some studies, such substances cause little concern for the safety of the host’s system. There are, however, reasons to believe that substances entering the system of a person, little as they are, could present considerable risks for cancer development. Therefore, they are of importance. DDT falls under this category because the amounts that enter the human system upon skin exposure are not enough to warrant any significant health measures, but they could present a potential carcinogenic risk.
Disposition of toxic compound
Disposition of toxic compounds is usually a four step process involving absorption, distribution, metabolism and excretion. With a proper understanding of these four processes within the disposition process, it is possible to make a fairly objective and accurate projection as to whether or not a compound is safe for human consumption.
DDT is no exception to the four-step disposition process of all toxic compounds. The absorption of DDT requires that it passes through the membranes of the body. Absorption usually occurs through body membranes such as the integument and membranes lining both the respiratory and digestive tracts. DDT particles are so large that when inhaled, they get deposited in the upper respiratory tract and are eventually swallowed (Besbelli, 1990). DDT is absorbed very slowly form the digestive tract, but its dissolution in animal or vegetable fats makes it more easily absorbed. Its dermal absorption is limited. Hence, from an absorptive point of view, DDT seems not to be easily absorbed.
DDT is quickly distributed throughout the body via the bloodstream after absorption, and it can thus present major toxicity within a short period of time. It has been identified in all body tissues after its administration, suggesting that it can be stored in all body tissues. The chemical has been shown to have a preference for storage in adipose tissue due to its fat-solubility.
The half-life of DDT is long and could be months long. Adipose-stored DDT has been shown to be lost slowly form the system after a cessation of ingestion, and about 25.5 months after cessation of ingestion, the amounts found in the adipose could still be about 35% of the total amount ingested (Besbelli, 1990). DDT is usually converted to the less toxic form, DDE, but the storage time for this compound within body tissues is infinite. However, the major pathway for detoxification of DDT is through its conversion to DDD, and finally to a water soluble compound, DDA, which is much more easily excreted from the system.
DDT is slowly excreted from the system with about only 1% of stored DDT getting excreted from the system daily. It is mainly excreted in the form of DDA. It is excreted through the urine and also through milk. It can also be transferred through the placenta.
DDT can be lethal in doses of about 30 g for an adult human being. Fats and oils increase its toxicity because they aid in its absorption. The relatively long half-life of DDT in human beings could increase its potential danger because it could have a carcinogenic effect.
Exposure and Responses
DDT can gain access to the body through a number of means. It could accidentally or deliberately get ingested through the mouth, or through contaminated foodstuffs. The chemical could get inhaled through occupational exposure or otherwise. DDT is poorly absorbed through the integument, although oily skin could enhance its absorption. The chemical might also be transferred through breastfeeding of milk from mother to infant or through the placenta from mother to fetus.
Poisoning by DDT often displays clinical symptoms over a wide range of time, depending on how much exposure has been achieved by the patient. The patient may vomit immediately due to local gastric reflexes. The symptoms may start showing after as many as six hours. Common signs of DDT poisoning include: vomiting, dizziness, loss of equilibrium, ataxia and convulsions.
Should WHO Continue to Approve of DDT?
DDT is indeed an effective control against malaria. However, the positive effect of DDT in the fight against malaria could be counterbalanced or even surpassed by its negative effects on the human population. For instance, the increase in infant survival due to malaria control could be offset by the infant mortality resulting from decreased lactation or preterm birth, both of which have been attributed to DDT(Van Den Berg, 2009). Therefore, the WHO ought to consider reviewing its policy regarding DDT.