Exploring The Use Of Dichlorodiphenyltrichloroethane Biology Essay

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For malaria vector control, DDT is spread in Mauritius regularly at the seaport and airport areas and on one-shot case-to-case basis in areas where malaria case is reported. Mauritius has been declared as a malaria-free zone since 1973 but there are traces which sometimes occur due to flooding or after the passage of a cyclone when isolated endemic cases become prevalent. However, reported cases of malaria, in recent years, are mostly imported ones: either by Mauritians who have visited malaria-prone areas or foreigners coming from such areas and visiting the country. This is why DDT is sprayed regularly (every 6 months) at the ports of entry which are the Sir SeewosagurRamgoolam Airport at Plaisance and the seaport in Port-Louis.

Since 1998, cases of malaria reported have been only imported and not indigenous. In 2004, there were five cases detected in the district of Port-Louis, namely at Vallee Pitot, Tranquebar and Vallee des Pretres, but these were again secondary cases introduced by foreign contacts. The reduction in the number of cases of indigenous malaria reported in recent years has led to a significant decline in the amount of DDT applied per annum: from five tons a year in the 80s to some 500Kgs in 2010! The current stock of DDT stands at 121 tons and is kept under highly questionable conditions.

Exposure to DDT may have serious health effects on human beings and the environment itself. It has been found that the stock of DDT is high and that it is dated as far as the early 80s. Hence, it could be a major threat to workers who run the risk of being contaminated whenever they need to have access to the stores where the DDT stockpile is kept and whenever they have to spray the pollutant. Unawareness may increase their vulnerability as well as for those who may be in contact with the proliferation of DDT, either sprayers or bystanders (for example, local habitants), by the way of transportation through the medium of air. To cite an example, local inhabitants might not always be kept informed of the spraying of DDT in and around canals or rivers where malaria is suspected. Since the regions at risk are the

Airport and the seaport, this implies that several individuals, besides workers, do run the risk of coming into contact with DDT.

It is also important to note that non-target species and complete ecosystems could easily be at risk with the spraying of DDT. Through air transportation, birds and plants could be seriously affected, especially at the airport's vicinities, which is an agricultural area. At the seaport, the runoffs into the sea would constitute a potential threat to the marine environment. Constant spraying may have serious implications for marine life.

Even if there is practically no malaria in the country, control at the ports remains a major task. Foreign pests and diseases may penetrate the country through aircrafts and ships and this is why spraying is required to safeguard the Mauritian natural environment. One major reason that would explain the frequent use of DDT is because the current stock was obtained at no cost and was large enough to serve as vector control for several years. DDT has therefore played a major role to ensure the socio-economic progress of the country. Now that malaria has considerably decreased, it makes little sense to maintain such a high stock of contaminated DDT for vector control.

However, alternatives to DDT could be introduced, for instance, by synthetic pyrethroids and by the use of bed nets treated with alternative chemicals in order, to reduce the health risks involved and potential damages to the environment as a whole. If no action is taken regarding DDT, then we could expect, among the major cases of exposure, an increase in food contamination, dermatological and respiratory problems and, worse, should pregnant women be exposed, there would be complications such as foetal growth disorders for pregnant women/girls.

Due to its large stockpile, the DDT problem is the biggest by magnitude and there are also analysis reports indicating that the stockpiles have contaminated areas around the storage sites4.

While there is an on-going discussion about the timeline, there is consensus that steps should be taken for investigating how the use of DDT could be discontinued and the use of alternative chemicals and practices would be established.

Before the switching to non-Persistent Organic Pollutants (POPs) alternatives may happen, risky practices still exist in handling, application and the stock- keeping stages of the existing DDT. In order to mitigate these risks, the personnel in contact with DDT will need training in safer practices.

DDT is found in the list of prohibited chemicals (18th Schedule, section 27, part ii of Dangerous Chemicals Control Act (DCC Act) 2004.

2.1.1 Stakeholders involved in DDT use

ACTIVITY

STAKEHOLDER(S)

Distribution and Storage

Government of Mauritius (Ministry of Health and Quality of Life) and Workers.

Source of Production

Donated: Imported.

Externality Effect

Civil Society, particularly in marshy areas.

Particular Spraying Areas

Airport Authorities and Seaport Authorities, Ministry of Environment &NDU

In the above table, the externality effect refers to the second-round effect following the action of spraying which may affect any individual in contact with the spraying of DDT and who require medical treatment was also found, though of a relatively much lower degree of concern, that the storage conditions of DDT was inappropriate.

The Ministry of Health and Quality of Life has since centralized all the stock of DDT to Pamplemousses (Powder Mill) but the fencing need to be reinforced so as to prevent people from having access to the site. Furthermore, it was found that the soil around the stores where DDT is kept is quite contaminated4. Needless to say, this could be easily carried away during heavy rains that would further spread the pollutant to other compounds, constituting thus a threat to agriculture.

2.1.2 Current Practices for DDT Stocks

DDT is used currently only in malaria control and has been banned as an agricultural pesticide. Around one ton of DDT is used per year in Mauritius and there are two forms of DDT: in powder and in flakes. Among the 121 tons of DDT, there is 92 tons in powder form and 29 tons in the form of flakes which is used for indoor residual spraying. The DDT powder is mixed with water before it is used for spraying on flammable materials whereas the DDT flakes is boiled with petrol, in usually a drum, prior to be used for spraying on non-flammable materials. It is sprayed in regions/areas when there are risks of transmission and as a preventive measure, at the airport and the seaport.

The stockpile of DDT was repacked and storage centralized at Pamplemousses Powder Mill in January 2005 as conditions of storage at Fort George and Mahebourg Community Hospital were not satisfactory.

At present, there are 121 tons of DDT which are available from stocks dating as far back as 1982 and 1983 but as per efficacy tests, DDT flakes is still at 79% and DDT powder is at 56%4. However, while analysing the breakdown rates, it is seen that the flake formulation has deteriorated beyond any possibilities for reuse and the powder formulation has also started to decompose. Therefore, the DDT stocks can neither be reformulated nor re-exported for future use.

The totality of the DDT is now stored at the powder mill in Pamplemousses. The premises are not properly fenced and to the public may get access to it.

As a measure of prevention, the Ministry of Health officials must carry out a very effective exercise to remove stagnant water on the roofs of houses and in the backyards in order to reduce the breeding of malaria-mosquitoes, thus indirectly reducing need for vector control.

The Republic of Mauritius signed the Stockholm Convention on POPs on 23 May 2001,ratified it on 13 July 2004 and is committed to comply with its provisions.Mauritius has been granted an exemption for the use of DDT (1,500Kg per annum) in malaria control by the Stockholm Convention Secretariat in 2004 for over three (3) years. However, an action plan should be developed for the reduction in reliance on DDT and on its eventual/possible replacement by safer alternatives.

2.2 Role of the Ministry of Health and Quality of Life

The Ministry of Health and Quality of Life (MOH) is the main regulatory body that controls, under the DCC Act 2004, all dangerous and extremely dangerous chemicals throughout their different stages of life: import, export, transit, production, sale, distribution, transport, storage and disposal. As an enforcing agency under the DCC Act 2004, it is specifically responsible for health effects consequential to accidental, occupational or environmental exposure to dangerous chemicals, medical surveillance and regular medical examinations. The Ministry is also responsible for regular investigation of occupational diseases or work related diseases following exposure to, or the use of, dangerous chemicals.

The Ministry of Health acts as the main coordinating body with other organisations in the management of dangerous chemicals and provides the secretariat facilities for the functioning of the Dangerous Chemicals Control Board (DCCB) set up under the DCC Act 2004. Through the DCCB, the MOH is responsible for carrying out the following functions:

Register all importers, manufacturers, distributors and retailers of dangerous chemicals;

Register all chemicals manufactured, imported and sold in Mauiritius.

Issue licences for the manufacture, import, export, retailing, transport and storage of chemicals;

Issue of permits for the import of highly dangerous chemicals and pesticides;

Classify all chemicals according to schedules;

Ensure compliance with different sections of the legislations especially on labeling and packaging;

Ensure proper coordination among the different enforcing agencies;

Prepare guidelines, codes of practice and regulations on dangerous chemicals;

Disseminate information on chemicals to the public;

Receive notifications on import of dangerous chemicals;

Prepare a Register of dangerous chemicals.

The Ministry of Health is also the authority responsible for determining and enforcing the maximum pesticide residue limits in food under the Food Act.

2.3 The Dangerous Chemicals Control Act (DCC) 2004

The main objective of the DCC Act 2004 was to provide a better legal framework for the control of dangerous chemicals in order to prevent damage to health and to the environment by chemical substances and to provide for better protection of workers, members of the public and the environment. The Act however does not apply to prepared processed or prepared foodstuff and to biological agents other than those used as pesticides. The Pesticides Control Act 1972 was repealed by the DCC Act 2004.

Section 23 of the DCC Act provides that "every person who imports, produces, manufactures or sells any commodity for human or animal consumption shall ensure that the commodity marketed or sold (…..) presents no danger to the health of consumers by reason of toxic residues contained in or on such commodity through the use of pesticides or other dangerous chemicals on crops or otherwise (…..)". But some caution need to be taken as, according to Section 27(2) of the Act, anyone may freely import, manufacture, use or possess a prohibited chemical if it is for research purposes, experiments or as a reference sample or exhibit.

The Act divides chemicals into four groups according to the level of risk they pose:

1. Non-dangerous chemicals for which export, import, sales, distribution and manufacturing is not restricted.

2. Dangerous chemicals for which export, import, sales, distribution and manufacturing require a general licence.

3. Pesticides and extremely dangerous chemicals, a category of highly risky dangerous chemicals and pesticides that require a permit on a chemical-by-chemical basis.

4. Prohibited chemicals which are not be subject to export, import, sales, distribution or manufacturing

The DCC Act also requires in paragraph 19, to substitute a dangerous chemical with a less dangerous alternative if available. This would facilitate the withdrawal of risky chemicals from the market and replace those with other products. Such provisions may be of importance if and when new chemicals are identified.

The Pesticides Control Board was previously responsible for the control of import and use of pesticides in Mauritius. It has been replaced by the Dangerous Chemicals Advisory Council and the Dangerous Chemicals Control Board, in accordance with the Dangerous Chemicals Control Act 2004.

2.4 The Food Act 1998

A few Regulations of the Food Act 1998 do also mention pesticides. In the Tenth Schedule (Regulations 62(2)(d) entitled Maximum Pesticide Residues in Food, there are maximum residue limits for Heptachlor that read as follows:

- 0.2 mg/kg for carrots and carcass meat (in fat);

- 0.02 mg/kg for raw cereals and tomatoes;

- 0.05 mg/kg for vegetables.

In the 64th Schedule of the Food Act (Regulation 421), Guidelines Values for Bottle Water, standards are set for the following pesticides:

Aldrin and Dieldrin 0.03 microgram/1

DDT 1 microgram/1

HCB 1 microgram/1

Heptachlor

(and Heptachlor Oxide) 0.03 microgram/1

2.5 WHAT IS CHOLINESTERASE ?

Cholinesterase is one of many important enzymes needed for the proper functioning of the nervous systems of humans. Certain chemical classes of pesticides, such as organophosphates (Ops) &carbamates (CMs), work against undesirable bugs by interfering with, or 'inhibiting' cholinesterase. While the effects of cholinesterase inhibiting products are intended for insect pests, these chemicals can also be poisonous, or toxic, to humans in some situations.

Human exposure to cholinesterase inhibiting chemicals can result from inhalation, ingestion or eye or skin contact during the manufacture, mixing or applications of these pesticides.

Figure 5 Point of entry

2.5.1 HOW DOES IT WORK?

Electrical switching centers, called 'synapses' are found throughout the nervous systems of humans. Muscles, glands, and nerve fibers called 'neurons' are stimulated or inhibited by the constant firing of signals across these synapses. Stimulating signals are usually carried by a chemical called 'acetylcholine'. Stimulating signals are discontinued by a specific type of cholinesterase enzyme, acetylcholinesterase, which breaks down the acetylcholine. These important chemical reactions are usually going on all the time at a very fast rate, with acetylcholine causing stimulation and acetylcholinesterase ending the signal. If cholinesterase-affecting insecticides are present in the synapses, however, this situation is thrown out of balance. The presence of cholinesterase inhibiting chemicals prevents the breakdown of acetylcholine. Acetylcholine can then build up, causing a "jam" in the nervous system. Thus, when a person receives too great an exposure to cholinesterase inhibiting compounds, the body is unable to break down the acetylcholine.

Exposure to:

carbamates

organophosphates

May result in:

build-up of acetylcholine

cholinesterase inhibition

constant firing of electrical messages

potential symptoms of: twitching, trembling, paralysed breathing, convulsion, and in extreme cases, death.

2.5.2 WHICH PESTICIDES CAN INHIBIT CHOLINESTERASE ?

Any pesticide that can bind or inhibit, cholinesterase, making it unable to breakdown acetylcholine, is called a "cholinesterase inhibitor" or "anticholinesterase agent". The two main classes of cholinesterase inhibiting pesticides are the organophosphates (Ops) and the carbamates (CMs).

Organophosphate insecticides include some of the most toxic pesticides. They can enter the human body through skin absorption, inhalation and ingestion. They can affect cholinesterase activity in both red blood cells and in blood plasma, and can act directly, or in combination with other enzymes, on cholinesterase in the body. The following list includes some of the most commonly used Ops:

acephate (Orthene)

fensulfothion (Dasanit)

Aspon

fenthion (Baytex, Tiguvon)

azinphos-methyl (Guthion)

fonofos (Dyfonate)

carbofuran (Furadan, F formulation)

isofenfos (Oftanol, Amaze)

carbophenothion (Trithion)

malathion (Cythion)

chlorfenvinphos (Birlane)

methamidophos (Monitor)

chlorphyrifos (Dursban, Lorsban)

methidathion (Supracide)

coumaphos (Co-Ral)

methyl parathion

crotoxyphos (Ciodrin, Ciovap)

mevinphos (Phosdrin)

crufomate (Ruelene)

monocrotophos

demeton (Systox)

naled (Dibrom)

diazinon (Spectracide)

oxydemeton-methyl (Meta systox-R)

dichlorvos (DDVP, Vapona)

parathion (Niran, Phoskil)

dicrotophos (Bidrin)

phorate (Thimet)

dimethoate (Cygon, De-Fend)

phosalone (Zolonc)

dioxathion (Delnav)

phosmet (Irnidan, Prolate)

disulfoton (Di-Syston)

phosphamidon(Dimecron)

EPN

Temephos (Abate)

ethion

TEPP

ethoprop (Mocap)

terbufos (Counter)

famphur

tetrachlorvinphos

fenamiphos (Nemacur)

trichlorfon (Dylox, Neguvon)

fenitrothion (Sumithion)

Carbamates, like organophosphates, vary widely in toxicity and work by inhibiting plasma cholinesterase. Some examples of carbamates are listed below:

aldicarb (Temik)

oxamyl (Vydate)

bendiocarb (Ficam)

pinmicarb(Pirimor)

bufencarb

propoxur (Baygon)

carbaryl (Sevin)

carbofurant (Furadan)

formetanate (Carzol)

methiocarb (Mesurol)

methomul (Lannate, Nudrin)

2.5.3 WHAT HAPPENS AS A RESULT OF OVEREXPOSURE TO CHOLINESTERASE INHIBITING PESTICIDES ?

Overexposure to organophosphate and carbamate insecticides can result in cholinesterase inhibition. These pesticides combine with acetylcholinesterase at nerve endings in the brain and nervous system, and with other types of cholinesterase found in the blood. This allows acetylcholine to build up, while protective levels of the cholinesterase enzyme decrease. The more cholinesterase levels decrease, the more likely symptoms of poisoning from cholinesterase inhibiting pesticides are to show.

Signs and symptoms of cholinesterase inhibition from exposure to CMs or Ops include the following:

In mild cases (within 4 - 24 hours of contact): tiredness, weakness, dizziness, nausea and blurred vision;

In moderate cases (within 4 - 24 hours of contact): headache, sweating, tearing, drooling, vomiting, tunnel vision, and twitching;

In severe cases (after continued daily absorption): abdominal cramps, urinating, diarrhea, muscular tremors, staggering gait, pinpoint pupils, hypotension (abnormally low blood pressure), slow heartbeat, breathing difficulty, and possibly death, if not promptly treated by a physician.

FIGURE 6 .SYMPTOMS OF PESTICIDE POISONING. Source: Pesticide Education Manual: A Guide to Safe Use and Handling. Pennsylvania State University.

The types and severity of cholinesterase inhibition symptoms depend on:

the toxicity of the pesticide.

the amount of pesticide involved in the exposure.

the route of exposure.

the duration of exposure.

FIGURE 7. Rates of absorption in the human body depend on the pesticide formulation and the exposed areas of the body.

Source: The Safe and Effective Use of Pesticides. 1988. University of California, Publication 3324.

Figure 8 Areas that absorb chemicals quickly

Although the signs of cholinesterase inhibition are similar for both carbamate and organophosphate poisoning, blood cholinesterase returns to safe levels much more quickly after exposure to CMs than after OP exposure. Depending on the degree of exposure cholinesterase levels may return to pre-exposure levels after a period ranging from several hours to several days for carbamate exposure, and from a few days to several weeks for organophosphates.

If someone experiences any of these symptoms, especially a combination of four or more of these symptoms during pesticide handling or through other sources of exposure, they should immediately remove themselves from possible further exposure. Work should not be started again until first aid or medical attention is given and the work area has been decontaminated. Work practices, possible sources of exposure, and protective precautions should also be carefully examined.

The victim of poisoning should be transported to the nearest hospital at the first sign(s) of poisoning. Atropine and pralidoxime (2- PAM, Protopam) chloride may be given by the physician for organophosphate poisoning; atropine is the only antidote needed to treat cholinesterase inhibition resulting from carbamate exposure7.

2.5.4 WHY MONITOR CHOLINESTERASE ?

Anyone exposed to cholinesterase-affected pesticides can develop lowered cholinesterase levels. The purpose of regular checking of cholinesterase levels is to alert the exposed person to any change in the level of this essential enzyme before it can cause serious illness. Ideally, a pre-exposure baseline cholinesterase value should be established for any individual before they come in regular contact with organophosphates and carbamates. Fortunately, the breakdown of cholinesterase can be reversed and cholinesterase levels will return to normal if pesticide exposure is stopped.

2.5.5 WHAT IS THE CHOLINESTERASE TEST?

Humans have three types of cholinesterase: red blood cell (RBC) cholinesterase, called "true cholinesterase;" plasma cholinesterase, called "pseudocholinesterase;" and brain cholinesterase. Red blood cell cholinesterase is the same enzyme that is found in the nervous system, while plasma cholinesterase is made in the liver.

When a cholinesterase blood test is taken, two types of cholinesterase can be detected. Physicians find plasma cholinesterase readings helpful for detecting the early, acute effects of organophosphate poisoning, while red blood cell readings are useful in evaluating long-term, or chronic, exposure6.

The cholinesterase test is a blood test used to measure the effect of exposure to certain or cholinesterase-affected insecticides. Both plasma (or serum) and red blood cell (RBC) cholinesterase should be tested. These two tests have different meanings and the combined report is needed by the physician for a complete understanding of the individual's particular cholinesterase situation.

2.5.6 The Rapid Field Determination of Cholinesterase (use by Government Analyst Division)

Introduction

Farmers, spray operators, and research workers using organic phosphorus insecticides may run some risk of significant absorption of these toxic chemicals despite the adoption of protective measures. Over-absorption, and unsafe working methods, are detectable by depression of the normal cholinesterase enzyme activity of the blood. Several methods exist for the accurate measurement in the laboratory of cholinesterase activity, but a rapid 'field' method is frequentlyneeded for use in emergencies or away from the laboratory. The method of Limperos and Ranta8has been modified by Edson9to give a combination of speed, convenience and reasonable precision for emergency or routine cholinesterase determination with simple equipment.

The cholinesterase activity in the blood from the subject under test is expressed as a percentage of the activity in normal blood. Depending on the result obtained, the following action is recommended.

100% - 75 % of normal no action, but retest in near future.

75% - 50% of normal Over-exposure probable; repeat test. If confirmed, suspendfrom further work with organic phosphorus insecticides for2 weeks; then retest to assess recovery.

50% - 25% of normal Serious over-exposure: repeat test. If confirmed, suspend

from all work with insecticides. If indisposed or ill arrange medical examination.

25% - 0% of normal Very serious and dangerous over-exposure. Repeat test: if

confirmed, suspend from all work pending medical

examination.

Principle of the method

Blood contains an enzyme, cholinesterase, which liberates acetic acid from acetylcholine thereby changing the pH. A mixture of blood, indicator and acetylcholine perchlorate is prepared and allowed to stand for a fixed time. The change of pH in this time is a measure of the cholinesterase activity.

It has been established by Watson & Edson10 that, as suggested by Davies & Nicholls11 it is possible to dispense with a timed control sample and to substitute a temperature/time relationship provided that the temperature range involved is not excessive and that the modified instructions are followed exactly.

Reagents required

1. Indicator solution

Sodium salt of bromo-thymol blue (B.D.H. Ltd. Water soluble) 0.25g.

Distilled water (CO2 free) 560ml.

This solution is stable for several months and should be kept tightly stoppered to prevent

Absorption of CO2 . The concentration is critical, the permissible limits being + 0.01g.

2. Substrate solution

Acetylcholine perchlorate 0.5 + 0.2 gm.

Distilled water (CO2 free) 100ml.

This substrate solution should be freshly prepared each day. The exact concentration is not critical, and slight turbidity can be ignored.

The Standard Lovibond Comparator Disc 5/30

The disc covers the range 0-100% normal activity in steps of 121/2%, and is calibrated for use with 2.5mm. cells.

Technique

(a) Determination of blood cholinesterase in human beings

1. Test the reagents by mixing 0.5ml. of indicator, 0.01 ml. of finger-prick blood from a normal "control" subject, and 0.5ml. of substrate solution. Mix well and place in a 2.5mm. cell in the right-hand compartment of the comparator. Hold the comparator facing a source of uniform light, such as the north sky in the northern hemisphere and revolve the disc until a close colour match with the test solution is obtained. It should be no more yellow (acid) than the 12.5% activity colour. If the indicator solution is too acid, due to the absorption of carbon dioxide, it can be restored to normality by bringing it momentarily to the boil. If this does not reduce acidity to the 12.5% colour the substrate is at fault and it must be discarded and a fresh solution prepared.

2. Make a blood "blank" by adding 0.01ml. of finger-prick blood to 1 ml. distilled water in a 2.5mm. cell and place in the left-hand compartment of the comparator.

3. Set up a reaction tube for each patient, and pipette 0.5ml. of indicator solution into each tube. Up to 15-20 tests can be carried out at the same time.

4. From each patient pipette 0.01 ml blood, obtained by finger or thumb prick, into a reaction tube, rinsing the pipette two or three times with the indicator in the tube. A

"control" blood sample (i.e. that of a normally healthy person unexposed to organic phosphorus insecticides) should be put into tube No. 1.

5. Pipette 0.5ml. substrate solution into tube No. 1 ("control" tube). Note the time ("zero time"), immediately transfer the reaction mixture to a 2.5mm. cell and note its colour in the comparator. It should be no more acid than the 12.5% colour.

6. Add 0.5ml. substrate solution to the other reaction tubes at 1 minute intervals from zero time, stopper them and shake to mix.

7. Wait for the contents of the control sample cell to reach 100% activity colour (which will take 20-30 minutes, depending largely on temperature) decant control sample and at 1 minutes intervals from this time transfer the contents of the other tubes in turn to the cell. Match each sample against the disc, by placing the cell in the right-hand compartment of the comparator and revolving the disc until the nearest match is found, and record the activity. The discs are graduated in % of normal (i.e. of control) activity.

(b) Simplified Technique

Test the reagents, make up a blood blank, set up the reaction tubes as directed in paragraphs 1-3 of the original instructions. From each patient pipette into a reaction tube 0.01ml. of blood, obtained by finger or thumb prick, rinsing the pipette two or three times with the indicator in the tube. Note the shade temperature. Add 0.5ml. of substrate to the reactions tubes at 1 minute intervals, stopper the tubes and shake to mix. Allow each tube to stand for exactly the time corresponding to the shade temperature shown in the Table. Immediately this time has expired transfer the contents of the tube to the 2.5mm. sample cell, place this in the right-hand compartment of the comparator and match against the standards in the disc.

Time-Temperature Table (Table 2)

Use time column corresponding most closely to colour value in reagent test

Time minutes

Shade Temp. oC Reagent =0% Reagent=121/2%

10 41 36

15 33 29 20 27 24

25 24 21

30 21 18.5

35 18 16

40 16.5 14.5

45 16 14

For temperatures above 45oC the original procedure must be used.

Notes

Good agreement has been found with results obtained by the electrometric method of Michel12

Acid, alkali or insecticide contamination should be avoided by carefully cleaning the skin before taking the blood sample, first with soap and water, then with surgical spirit, and drying the area with clean cotton wool. The needle must also be carefully cleaned each time.

The control blood sample must be obtained from a normally healthy person, who has had no probability of exposure to organic phosphorus insecticides in the past three months. Alternatively, a 'stock' sample of normal blood may be used, but only heparin is suitable for use as the anticoagulant. Citrate or oxalate cause interfering pH changes and should not be used.

The reaction tubes and bungs must be carefully washed with distilled water between tests, because, as this test depends on a change of pH, there must be no contamination from any acid or alkali.

.All pipetting must be done with teats to avoid producing acidity and false results due to contamination with CO2 in the breath.

The 100% normal cholinesterase value of the cholinesterase disc is based on average values for healthy European males. Non-Europeans of tropical countries may show lower normal values, in the range of 75-87%. Females normally have slightly lower ChE activity than males.

As there is considerable personal variation in normal blood ChE activity, it is very desirable wherever possible, to determine the normal activity of all workers before they begin a campaign with organic phosphorus insecticides.

The indicator-blood dilution is stable only for up to four hours in cool climates, and two hours in hot climates. Individual 0.01ml. blood samples from isolated workers may thus be collected and retained in stoppered reaction tubes, as dilution in 0.5ml. indicator solution, but should be analysed within the above times.

An almost immediate colour change from green-blue to orange suggests acid contamination. Repeat the test after washing out tubes with distilled water.

Failure to develop any colour change in the reaction tube may be due to a complete absence of cholinesterase in the blood sample from a grossly over-exposed worker, but may also be due to failure to add the blood or substrate, or to alkaline contamination. All such instances therefore necessitate a repeat test for confirmation.

A portable field set is available for use with this test.

2.5.7 WHO NEEDS TO BE TESTED

The following people should be concerned with having their cholinesterase levels checked on a regular basis: (a) anyone that mixes, loads, applies, or expects to handle or come in contact with highly or moderately toxic organophosphate and/or carbamate pesticides (this includes anyone servicing equipment used in the process); (b) anyone that is in contact with these chemicals for more than 36 hours at a time in one 14-day period.

In the Dangerous Chemicals Control Act (DCC Act)-2004 in the 12th schedule (Section 20) Part 2(1) (b) regarding examination of worker requires that no person shall be employed in the manufacture or processing of any dangerous chemical or on a scheduled operation unless that person is in possession of a medical certificate indicating the level of cholinesterase in his blood or any other appropriate test result.

Part 4- where the level of cholinesterase in the blood of an employee is less than 60% of the highest level recorded for that employee in the preceding 12 months, the employer shall not cause or permit that employee to be exposed to a pesticide or to any other cholinesterase inhibiting substance unless:-

theauthorised officer has certified in writing that the employee is fit to be exposed to such pesticide and other cholinesterase inhibiting substance; and

not less than 2 weeks have elapsed since the employee was last so exposed.

Part 8- (restriction on hours of works for pesticide workers) provides for:

No worker shall be employed on a scheduled operation for more than:

6 hours in one day;

36 hours in a period of 14 days

In the DCC Act , 2nd schedule, (section 2), Temephos is classified in the list of extremely dangerous chemicals (restricted) - Part II - Agricultural Chemicals. Therefore, the provision of Part 8 in the 12th schedule on the restriction on hours of work for pesticide workers is not being respected as the workers are employed on a full-time basis as sprayerman in the Ministry of Health and plays a vital role in the control of insect-borne diseases like Malaria, Chikungunya and Dengue fever in the country.

Presently, no pre-employment testing of blood cholinesterase level is carried out for sprayermen upon joining the service as per provision of Part 2(1)(b) of 12th schedule (Section 20) of DCC Act which does not allow to establish baseline data for each individual worker for future comparison and this section for all workers employed in the manufacture or processing of any dangerous chemical or on a scheduled operation to have their blood cholinesterase level tested and not only those expose to carbamates and organophosphates.

The cholinesterase control program in Mauritius should include workers expose to industrial and agricultural chemicals which are of the classes of Organophosphates (Ops)andCarbamates (CMs) as these are known cholinesterase inhibiting chemicals.

2.5.8 WHEN SHOULD SOMEONE BE TESTED AND HOW OFTEN?

Every person has his/her own individual 'normal' range of baseline cholinesterase values; cholinesterase levels vary greatly within an individual, between individuals.

The extent of potential pesticide poisoning can be better understood if cholinesterase tests taken after exposure to the cholinesterase inhibiting pesticides can be compared to the individual's baseline, pre-exposure measurement. Workers that receive routine exposure to organophosphate or carbamate pesticides should be offered an initial pre-employment check of their blood cholinesterase levels to establish "baseline values" prior to any exposure to these agrochemicals. If no pre-exposure value was obtained, however, the earliest cholinesterase value recorded can be used for later comparison. Excessive exposure to OPs and CMs depresses the cholinesterase so markedly that a diagnosis can also be made without previous baseline testing. If an individual's cholinesterase levels drop 30 percent below the original baseline level, immediate retesting should be done.

OSHA 2005 - part vii - section 77 (Health Surveillance) part 2 provides for medical surveillance of an employee who is exposed to a hazardous substance at intervals of not less than once every 6 months or at shorter intervals as the medical practitioner may advise.

2.5.9 HOW DOES SOMEONE GET TESTED?

The cholinesterase monitoring program for the Spayermen/General workers of the Ministry of Health and Quality of Life consists of having their blood cholinesterase levels checked every six (6) months - as per section 77(2) of OSHA 2005(medical surveillance) - after prescription by a Government Medical Officer(usually an Occupational Physician) and removal of blood samples by venipuncture, the drawing of blood from a vein by puncturing the vein with a needle attached to a collecting tube by the Nursing Officer in the nearest Health Centre. The samples are sent to the Government Analyst Division for testing and the results are sent to the Governmemt Medical Officer for interpretation and the workers are informed accordingly.

2.5.10 WHAT IS THE CURRENT STATUS OF CHOLINESTERASE SURVEILLANCE PROGRAMS?

The cholinesterase control program in Mauritius include workers expose to industrial and agricultural chemicals which are of the classes of Organophosphates (Ops) and Carbamates(CMs) as these are known cholinesterase inhibiting chemicals. About 2000-2500 workers are concerned for the different sectors. Previously, officers from the Government Analyst Division use to go on site to collect blood samples to be analysed by them but since 2008,the blood is removed at the nearest Health Centre after prescription by a Medical Officer and forwarded to their Division for testing. These include industrial workers from Roger Faydherbe, IBL, Robert Lemaire, etc, agricultural workers from the Ministry of Agriculture and AREU, and sugar factory workers involved in the use and handling of pesticides, and of course, sprayermen from the Ministry of Health. According to information gathered from the Government Analyst

Division, about 2-2.5% of the total number of workers tested annually have a lowered blood cholinesterase level.

2.5.11 HOW ARE THE TESTS INTERPRETED?

The interpretation of cholinesterase test results should be done by a physician. A 15 to 25 percent depression in cholinesterase means that slight poisoning has taken place. A 25 to 35 percent drop signals moderate poisoning, and a 35 to 50 percent decline in the cholinesterase readings indicates severe poisoning6.

If the report shows a worker's cholinesterase level has dropped 20 percent below his/her baseline in either plasma or RBC, he/she should be retested immediately. If the second test repeats the same low values, fault work practices should be carefully looked for and steps should be taken to correct them.

A 30 percent drop below the individual's baseline of RBC cholinesterase or plasma cholinesterase means that the individual should be removed from all exposure to organophosphates and carbamates, with the individual not being allowed to return until both level return to the pre-exposure baseline range. Removal from exposure means avoidance of areas where the materials are handled or mixed and avoidance of any contact with open containers or with equipment that is used for mixing, dusting or spraying organophosphates or carbamates. A worker removed from exposure to cholinesterase inhibitors may be employed at other types of work.

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