DTT Critique

Introduction

The Stockholm Convention on Persistent Organic Pollutants approved 12 insecticides alongside DTT during the May 2007 convention that brought together 147 countries. However, the exemption was granted for indoor use only owing to the lack a viable insecticide to combat vector borne diseases. Because of this serious lack of a viable alternative to effective malarial control DTT has played a crucial role in the control of malaria. DTT was recommended 12 alongside other insecticides for Indoor Residual Spraying (IRS) (WHO, 2007).

The Strengths of DTT

According to World Health Organization (2001), the residual effect of DTT has a length of 6 to 12 months compared to the other 12 recommended by the IRS. For instance, organophosphates and carbamates are known to have a residual effect of between 2-6 moths, while Parathyroid efficacy lies between 3-6 months. This figure clearly depicts that it will be more expensive to use these alternatives than DTT. Besides, DTT has high repellency rate against insecticides.

Concerns have been raised about the toxicity of DTT as a possible threat to human health given the studies that show how DTT has been accumulated in food chains including in humans. In collaboration with FAO, WHO held a meeting held in 2000 to assess the residual effects of insecticides that covered issues ranging from storage, potentiality of these residuals in mother’s milk and possible presence of carcinogens and toxicological information in hormones. No epidemiological data supported claims that residues accumulated in human bodies (Najera, 2001)

 However we are still reviewing new findings on the possible toxic effects. We are also working closely with scientists to agree on the best way of assessing the effects of DTT in residual areas. In the light of the arguments above WHO still does not find satisfactory finding to halt use of DTT but we will revise our stand if new viable findings and information comes up (WHO, 2007).

The four phases of disposition of a chemical compound with respect to DTT

According to Pharm (2002) there are four ways for the disposition of a compound. First, it involves chemical absorption into the body, and then chemicals are distributed within the body followed by chemical metabolism and lastly excreted through different channels to eject the chemical compound. Chemical may enter our bodies orally by way of digestive tract, through inhalation or through dermal contact. DTT is absorbed through membranes through diffusion, filtration or phagocytes process. Less soluble DTT soluble diffuses less through the membranes.

Since the fetus has little fats, its does not accumulate less lipophilic DTT. In case of inhalation especially among DTT operators, DTT has low blood solubility, the rate of transmission from air will therefore largely dependent on the blood flow. Therefore DTT is perfusion is limited. In case of good ventilation, the rate of respiration will be greatly reduced. Distribution is further complicated by low affinity of DTT. DTT cannot be bound by the proteins in plasma and epidemiological studies have not revealed satisfactory evidence disproof this. DTT being less lipophilic does not accumulate in the adipose tissue unlike other toxic compounds allaying fears that it could lead to long term toxicity.

No studies have shown that indeed DTT accumulates in human skeleton as the case of lead and other compounds. Before entering the Central Nervous System (CNS), chemicals must cross the blood brain barrier. And a compound must be highly soluble to gain entry. Flow of DTT into the CNS has not been reported because this process is further hampered by the ionization processes which reduces rate of passage. Highly lipophilic compounds are able to be transmitted via placenta but not the case with DTT. Furthermore the placenta possesses unique metabolizing ability capabilities against DTT.

Even after absorption of this chemical compounds they may either be excreted through the lungs, feaces, urine, sweat etc. Because DTT is easily ionized, it’s readily excreted through urine unlike other compounds that may be reabsorbed into plasma from nephron. DTT has a moderate molecular weight of about 188 which is below 300 making it to be easily excreted through the feaces.

However it important to point out that this insecticide must be used under strict guidelines issued by the Convention. WHO in supporting use of DTT will not be held accountable for inappropriate use which may cause food poisoning.

Exposure and responses associated with DTT

According to Reiner (2001) when the eukaryotic cells are exposed to DTT, formation of bonds with disulphide is inhibited in the endoplasmic reticulum. Exited proteins become less vulnerable. Therefore when one is exposed to DTT, creation of encystations-specific secretory vesicles (ESV’s) is reduced significantly by at least 85%. Subsequent exposure to DTT further eliminates ESV’s followed by drop in Cyst Wall Proteins (CWP). However DTT does not affect the whole protein secretion gateway.  DTT studies show presence of protein disulphide isomerases on ESV’s. It was found out that DTT did not activate UPR (Unfolded Protein Response).

Reasons why WHO should continue using DTT to combat Malaria

The best example to illustrate why WHO should continue using DTT is South Africa. When South Africa terminated the use of DTT in 1997 and switched to other alternative, Anopheles funestus parasite re-surfaced with resulting malaria prevalence. Therefore for lack of a viable alternative to combat malaria vectors, DTT has proved to be the best solution at the moment.  It is worth noting that WHO wholly supports safety of chemicals together with its sister organization UNEP. We should not make the mistake of resorting to other alternatives that may be ineffective or costly. Therefore the elimination of DTT must have a technical and financial backing because it’s the lack of these that has made DTT the best alternative so far.

References

WHO (2007). The Use of DDT in Malaria Vector Control. Retrieved 06^th March 2009 at http://www.who.int/malaria/docs/IRS/DDT/DDTposition.pdf

Najera J. (2001). Malaria vector control: insecticides for indoor residual spraying. Geneva, World Health Organization.

Reiner, D. (2001). Reversible interruption of Giardia lamblia cyst protein. Retrieved 06^th March 2009 at http://www3.interscience.wiley.com/journal/118985793/abstract?CRETRY=1&SRETRY=0

Pharm, J (2002). Disposition of Chemical Compounds. Retrieved 6^th March 2009 at

http://www.calstatela.edu/faculty/mchen/Disposition-of-Chemical-Compounds-Lecture.ppt