Risk Assessment and Cholinesterase Monitoring for workers exposed to Plant Protection Products in Locust Control in Niger

Karimoun Massalatchi Illyassou^1,2, Mamane Illa¹, Rabani Adamou¹*, Aboubacar Maitournam³, Abdou Baoua⁴

¹Université Abdou Moumouni, Faculté des Sciences et Techniques, Département de Chimie, Laboratoire de Matériaux, Eau et Environment (LAMEE), BP 10662, Niamey, Niger

²Gembloux Agro-Bio Tech/ULg, Laboratoire de Phytopharmacie, Passage des Déportés 2, Gembloux 5030, Belgium

³Université Abdou Moumouni, Faculté des Sciences et Techniques, Département de Maths-Informatique, Niamey, Niger

^1,⁴Centre National de Lutte Antiacridienne, Niamey/Niger

*Corresponding Author E-mail: rabadamou@gmail.com

Abstract:

Plant protection products are designed to fight against pests. Nevertheless, their misuses can have negative impacts both on human health and environment. In the present paper, according to the local practices, UK Predictive Operator Exposure Model (UK-POEM) was used to quantify the Potential Dermal Exposure (DPE) during mixing/loading and application processes of workers involved in locust control in Niger. Then, a spectrophotometric method using a device Kit Test Mate model 400 was used in situ to monitor their acetylcholinesterase (Ache) inhibition rate. The preliminary investigation has shown that organophosphate and pyrethroid are the most common active substances insecticides used. The predictive model results demonstrate that, the exposure levels vary from 0.1626 mg/kg bw/day to 9.4656 mg/kg bw/day for operators using a hand-held sprayer and from 0.1112 mg/kg bw/day to 6.4757 mg/kg bw/day for operators using a vehicle mounted sprayer. These values are several times higher than the Acceptable Operator Exposure Level (AOEL) for all active substances: 315 to 5540 times for hand-held sprayer and 92 to 4637 for vehicle mounted sprayer. Ache measurements before and after plant protection products handling have revealed that, sixty-seven percent (67%) of agents involved in locust control had their cholinesterase level lower than the normal, with an inhibition rate varying from 32 to 94%; confirming predictive UK-POEM results. Application of combined predictive model and Ache inhibition method in risk assessment show clearly the needs to drastically reduce locust control agents exposure to pesticides in Niger and other Sahel countries.

KEY WORDS: Plant protection products, locust control, Cholinesterase, UK-POEM,, Niger.

1. INTRODUCTION:

Agricultural products are subject to various parasitic attacks [1]. To reduce losses from crop pests and to keep crops healthy in order to ensure high crop yields, various plant protection products (PPPs) are used [1, 2, 3] . These substances can be chemicals or micro-organisms (including viruses) that have action against pests or on plants, part of plants or plant products [1, 4]. However, they can negatively impacted environment and human health [2, 5, 6, 7, 8]. Indeed, plant protection products generate high exposure for the farmers and for the consumers directly and/or via the presence of PPPs residues in harvested foodstuffs [9, 10, 11]. The principal’s routes of exposure of plant protection products for workers are during mixing/loading and application [12, 13, 3]. The consequences resulting from chronic exposure are many diseases and degenerative conditions such as cancer and Alzheimer’s [3]. For this reason, the estimation of operator’s exposure is a part of the risk assessment during registration of PPPs [1]. To evaluate PPPs ecotoxicological impacts, several methods such as models and biological monitoring have been used in recent years to estimate operator’s exposure [14, 15, 16]. The World Health Organization (WHO) has recommended the erythrocyte Ache dosage as reference method for chronic exposition risk assessment to organophosphates and carbamates insecticides [2].

In Niger, agriculture is the main economic activity of the country and employs more than 80% of the working population [17]. Persistent attacks of locusts which significantly reduce the production yield occurred these last decades. To improve or maintain production levels, the most control method applied is the use of chemicals as plant protection products (PPP) [18, 2]. An average of 130,000 liters of chemical pesticides are used annually to respond to locusts pressure [18, 2, 3] . In locust control, organophosphate and pyretroid insecticides are the most widely used [18, 2]. The uses of these acutely toxic substances will enhance the risk of exposure and adverse effects for target and non-target species [19]. Indeed, pyrethroids are known to disturb the sodium channels of insects, animals and humans nerves while organophosphates inhibit their cholinesterase enzyme good operation. The cholinesterase enzyme is an enzyme involved in the mechanism of nerve impulses transmission in the nervous [20]. Therefore, PPPs misuse can have serious negative impacts both on human health.

In the present study, exposure to plant protection products and related risk for operators in charge of locust control in Niger his evaluated and the related risk is assessed by using predictive model approach and in situ cholinesterase inhibition measurements.

2. MATERIALS AND METHODS:

2.1. Materials:

For the inventory of used pesticides and local pesticide management practices, a questionnaire taking into account relative aspects about plant protection products and their practices was preliminary administrated. Then, a FAO questionnaire on poisoning incident issued from the WHO Guidelines on developing a reporting system for health and environmental incidents resulting from Exposure to Pesticide is used to collect information regarding mainly the patient details, circumstances and activity at the time of exposure, route of exposure, identity and nature of the product, observed signs or symptoms of poisoning and severity grading, management and outcomes [21] . After a complete somatic clinical examination, especially on reflexes, for each agent, an individual sheet on cholinesterase activity were used to collect personal information (name, birth date, city and weight), Cholinesterase levels, the amount of hemoglobin and proposed actions.

A device Kit Test Mate model 400 was used for the monitoring of cholinesterase levels and the UK-POEM model was used to quantify the operator’s exposure during the plant protection management. The R software and hypothesis tests (Chi-square and Fisher) were used for the statistical analysis. All the collected data were preliminary tested for normality and the variances of Ache rates measured before and after pesticides handling processes were compared to identify bias between the two data collection processes. For graphing and additional data analysis, the software Origin 6.0 was used.

2.2. Methods:

2.2.1. Study area:

This study took place in Niger and concerned the plant management agents involved in locust control in all the country eight regions (figure 1). Sahelian and landlocked country with the closest point to the sea located approximately at 600 km, Niger covers an area of 1.267.000 km² and lies between longitudes 0° 16’ and 16° East and latitudes 11° 1’ and 23° 17’ North.. ¾ of the country are occupied by deserts. Most of the population (about 75%) being concentrated on 12% of the territory where agriculture is feasible. This region of the country is also the zone where locust’s pressure becomes more and more important. To fight against these pests, thousands of organophosphates, carbamates and pyrethroids pesticides are used each year.

Figure: Study area

2.2.2. Survey and collection of data:

An observation survey was first conducted to collect information on study population (persons involved in locust control in different regions). Then, a FAO questionnaire on poisoning incident was administrated to workers to collect data on individual characteristics. Finally, interviews were conducted among workers to collect data relatives to the following points:

· The treated location;

· The active substance characteristics;

· The profile of the person poisoned;

· The type of activity during exposure;

· The poisoning symptoms observed;

· The use of personal protective equipment;

· Etc.

Each person's cholinesterase data was recorded on an individual cholinesterase monitoring sheet provided by the locust control center of the country.

2.2.3. Blood sampling by finger puncture:

The Ache measurement related activities is conducted by a staff composed of researchers, Direction of Plant management (DPV) agents and physician of the ministry of health. The physician is responsible of the blood sampling. To ovoid absorption signal interferences during the Ache dosage, talcum powder-free vinyl gloves were used during all analytical procedures. to to handle the tube. The DPV has developed a standardized sampling method. A test tube containing 2 ml of surfactant phosphate and ethylene diamine acid (EDTA) as a buffer solution was introduced into the Test Mate® in order to calibrate the apparatus. The microprocessor updates and corrects its values according to the ambient temperature. This operation normally only takes 10 seconds, the tube is removed after the beep. Then, using a sterile lancet, a small incision is made on one of the fingers previously aseptised with alcohol 70°. The first drop of blood is cleaned with a compress. The second drop is gently removed (avoids air bubbles) taken with a microcapillary of 10 μl of volume. The heparinized microcapillary containing the 10 μl of blood is introduced into the buffer solution after stirring for 15 seconds so that the blood contained in the capillary dissipates in the buffer solution (EQM, 2003). The tube is then inserted into the apparatus, always taking care to align the capillary, to the materialized black point (key) on the Test Mate®. After the beep that intervenes 10 seconds later, the tube is removed. The reagent for the AChE, lyophilized substrate is dissolved with three drops of reactive solvent (distilled water + EDTA). The mixture is introduced into the tube containing the buffer solution and the 10 μl of blood, then slowly stirred (to prevent hemolysis) the tube for 5 seconds. The tube is re-inserted into the Test Mate® so that the capillary is superimposed on the key of the instrument. The procedures for the determination of AChE are carried out at ambient temperature of the laboratory (25 to 28°C) (EQM, 2003) [2].

2.3. Methodology of cholinesterase monitoring:

The determination of Acetylcholinesterase activity was carried out using a kit Test Mate model 400 (figure2). The main component of this kit is a photometric analyzer operating at a wavelength of 450 nanometers (figure 3). The method used to measure acetylcholinesterase activity has been described by Ellman et al., (1961) [22]. The reference values of erythrocyte acetylcholinesterase (AchE) and hemoglobin (Hb) of the device are derived from a series of test carried out by the designers of the device (EQM Research Inc. Cincinnati Ohio (USA)). These values are as follows:

· AChE = 4.71 U/ml ;

· Hb= 15.0 g/dl ;

· Q (AChE/Hb) = 31.4 U/g.

2.3.1. Dosage of cholinesterase:

In this study, only erythrocyte acetylcholinesterase was measured. Before monitoring occupational exposure of a person, the pre-exposure value of the cholinesterase has been determined. This value constitutes the reference value used as a basis for monitoring the evolution of the cholinesterase rate. For the post-exposure assay, sampling was carried out at the end of the campaign, after plant protection products handling.

2.3.2. Hazard characterization:

A rate of acetylcholinesterase inhibition between 20-30% indicates that the person is exposed to a cholinesterase inhibitor. When erythrocyte cholinesterase activity is reduced less than 50% of the normal, there is risk of clinical manifestations.

2.4. Model of workers exposure assessment:

The UK Predictive Operator Exposure Model (UK-POEM) was used in this study to quantify the Potential Dermal Exposure (PDE). The PDE was estimated during mixing/loading and application according to the local practices. In the application of the model, parameters including application method, formulation type, personal protective equipment, container type and active ingredient details are required. In this study, two exposure scenarios include the exposure of operators using a hand-held sprayer and the exposure of operators using a vehicle sprayer. The parameters used to assess the operators’ exposure for the two scenarios were presented in table 1 and 2. In estimation of operators exposure level to plant protection products, dermal absorption rate play a very important role. According to the PPR (Plant Protection Products and their Residues) panel group of EFSA, general default value (10%) was used to assess the exposure of workers involved in locust control in Niger. Two exposure scenarios, including exposure without Personal Protection Equipment (PPE) and exposure with PPE were assessed.

Table 1: Parameters used to calculate the exposure of operators using a hand-held sprayer

Parameters	Details
Application method	Hand-held sprayer (15 L tank)
Formulation type	Organic solvent-base
Dermal absorption from product	10%
Dermal absorption from spray	10%
Container	5 liters narrow closure
Work rate/day	1 hectare
Duration of spraying	6 hours
PPE	None/gloves

Table 2: Parameters used to calculate the exposure of operators using a vehicle sprayer

Parameters	Details
Application method	Tractor-mounted/trailed boom sprayer: rotary atomizers
Formulation type	Organic solvent-base
Dermal absorption from product	10%
Dermal absorption from spray	10%
Container	5 liters narrow closure
Work rate/day	50 hectares
Duration of spraying	6 hours
PPE	None/gloves

2.4.1. Risk assessment:

The risks of plant protection products were assessed by comparing the predicted exposure dose of every active ingredient expressed in milligram per kilogram of body weight per day (mg/Kg bw/day) with AOEL (Acceptable Operator Exposure Level). If the predicted exposure dose is lower than AOEL, it was judged to be safe. But if the predicted exposure dose is higher than AOEL, it was judged to be hazard.

2.5. Statistical analysis of data:

All results of survey sheets and the total exposure values were entered and analyzed using the software Origin version 6.0 and Excel 2007 software.

3. RESULTS:

3.1. Qualification of the study population:

A total of eighty-five (85) workers distributed in eight (8) regions of the country were surveyed. Among these 85 agents involved in locust control, 11 were supervisors, 8 prospectors-applicators, 29 driver-applicators, 10 phytosanitary-brigadiers, 15 loading-maneuvers, 7 storekeepers and 5 other agents (guards and secretary). The 77 male subjects were 44 ± 15 years old and had an average weight of 66 ± 16 kg. All the eight (8) women in this study showed no clinical sign of pregnancy, a physiological condition that could interfere with the cholinesterase assay [23, 24] . All subjects underwent consent after being informed and informed of the objective of the study, and guaranteeing the confidentiality of the data that is collected.

The distribution of agents by locality is shown in the table below.

Table 3: Agent qualification in locust control in Niger

Regions Qualification	Agadez	Diffa	Dosso	Maradi	Tahoua	Tillabery	Zinder	Niamey	Total
Supervisors	1	0	2	1	3	2	2	0	11
prospector-applicator	2	2	3	0	1	0	0000O	0	8
driver-applicator	9	2	2	3	3	2	1	7	29
phytosanitary-brigadier	4	0	2	0	1	1	2	0	10
loading-maneuver	1	1	0	7	2	3	1	0	15
Storekeeper	1	0	0	2	2	0	2	0	7
Others (gards and secretaries)	1	0	1	1	0	1	1	0	5
Total	19	5	10	14	12	9	9	7	85

Others: guard and secretary

3.2. Plant protection products inventory:

To fight against locust, plant protection products mostly used were organophosphate, pyrethroid and carbamate chemicals. In fact, 100% of the surveyed agents used these products. In total, nine (9) commercial formulations were inventoried during the survey and nine (9) active ingredients were identified (table 4). It was shown that the main categories of plant protection products used in Niger locust control were insecticides.

Table 4: Active ingredients used in locust control in Niger

Commercial formulation	Active ingredient	PPP category	PPPs family	Source of chemicals	WHO class
Karate 16,5 UL	Cyhalothrine	Insecticide	PYR	Syngenta	IV
Pyrical 480 UL	Chlorpiryfos-ethyl	Insecticide	OPs	ArystaLifeScience	II
Fyfanon 960 UL	Malathion	Insecticide	OPs	Cheminova SA	III
Decis 17,5 UL	Deltamethrine	Insecticide	PYR	Bayer Environ Science	IV
Queletox 640 UL	Fenthion	Avicide	OPs	Bayer Crop Sciences	II
Tracker 16,5 UL	Tralomethrine	Insecticide	PYR	ArystaLifeScience	IV
Sumithion L-100	Fenitrothion	Insecticide	OPs	Sumitomo Corporation	II
Unden 2DP	Propoxur	Insecticide	CAR	Bayer Crop Sciences	II
Dimethoate	Dimethoate	Insecticide	OPs	-	II

PYR: Pyrethroids; OPs: Organphosphate; CAR: Carbamate; EC: Emulsifiable Concentrate

UL: Ultra-Low volume; DP: Dustable Powder; -: No data provided

3.3. Practices of plant protection products use and management:

3.3.1. Use of Personal Protective Equipment:

In this study, various types of Personal Protective Equipment (PPE) were used by workers (figure 4).The individual protective equipments that were commonly used by workers were masks (11%), boots (7%) and sleeve shirts (4%). 19% of the workers don’t use any PPE during mixing/loading or spraying of plant protection products. Only 60% of surveyed workers wear full protection (figure 4).

Figure 4: Personal Protection Equipment used by workers

3.3.2. Poisoning symptoms by qualification:

Plant protection products are designed to fight against pests. Nevertheless they can also cause health effects in people. The gravity of the effects depends on the types of active ingredient and other chemicals that are in the products. With regard to these effects, some symptoms of plant protection products poisoning were reported by workers involved in locust control in Niger (figure 5). According to qualification, thirty-nine percent (39%) of applicators including prospector and driver declared that they had skin irritation, forty percent (40%) of phytosanitary brigadier had this symptom and twenty percent (20%) of them had headache after application (figure 5). Twenty percent (20%) declared respiratory problems and thirty-eight percent mentioned nose running (figure 5).

Figure 5: Poisoning symptoms

3.4. Cholinesterase monitoring of workers:

The results of cholinesterase monitoring of workers showed that sixty-seven percent (67%) of workers had cholinesterase inhibition after plant protection products handling. In fact, fifteen percent (15%) of surveyed workers had a cholinesterase inhibition between 20-30%, thirty-four percent (34%) had an inhibition between 30-50% and twenty-seven percent (27%) an inhibition greater than 50%. Only Twenty-four percent (24%) of workers with an inhbition rate less than 20%, had a normal cholinesterase value after chemicals handling (figure 6).

Figure 6: Cholinesterase inhibition after exposure

3.5. Exposure assessment by modeling:

The model used in this study to assess the operators’ exposure was the UK-POEM. Two exposure scenarios including exposure without personal protective equipment and exposure with full protection were evaluated. In total, eight (8) active substances were used in the model to generate the predicted exposure values during mixing/loading and spraying. The toxicity values of each active substance obtained through JMPR, Agrimex, EFSA and EU-Pesticides database are reported in table 5. The dermal absorption default value (10%) of each active substance is compared with the AOEL (Acceptable Operator Exposure Level).

Table 5: Toxicology properties of active ingredients

Active ingredients A.I	LD₅₀ (dermal) mg/kg.bw	AOEL mg/kg bw/day	Concentration g/L	Dose L/ha
Malathion	4100	0.03	960	2
Fenthion	345	0.007	640	0.3
Chlorpyrifos-Ethyl	2000	0.001	480	2
Tralomethrin	100	0,01	16.5	2
Deltamethrin	100	0.0075	17,5	3
Fenitrothion	>3000	0.013	1000	1
Dimethoate	>2000	0.001	400	0.55
Lambda-cyhalothrin	> 1754	0.0003	165	2.5

AOEL: Acceptable Operator Exposure Level; LD₅₀: Lethal Dose 50

The results of the modeling are given in form of figures.

3.5.1. Exposure of workers using a hand-held sprayer

Exposure without protection

Figure 7 shows the total potential exposure values of operators using a hand-held sprayer during mixing, loading and spraying without protection compared with the AOEL.

Figure 7: Total exposure without protection

Exposure with full protection:

Figure 8 shows the total potential exposure values of operators using a hand-held sprayer during mixing, loading and spraying with full protection compared with the AOEL.

Figure 8: Total exposure with full protection

3.5.2. Exposure of workers using a vehicle sprayer

Exposure without protection

Figure 9 shows the total potential exposure values of operators using a vehicle sprayer during mixing, loading and spraying without protection compared with the AOEL.

Figure 9: Total exposure without protection

Exposure with full protection

Figure 10 shows the total potential exposure values of operators using a vehicle sprayer during mixing, loading and spraying with full protection compared with the AOEL.

Figure 9: Total exposure without protection

4. DISCUSSION:

The principal active substances used in locust control in Niger are organophosphate and pyrethroid insecticides. The used of organophosphates formulations could be an important factor contributing to acetylcholinesterase inhibition [25, 26] . Many studies show that organophosphate insecticides can be rapidly absorbed through skin and mucous membranes or by inhalation. They are known to be specific inhibitors of acetylcholinesterase catalytic activity.

Personal Protective Equipment (PPE) for handling plant protection products includes protective clothing, boots, masks and gloves. In term of PPE, survey shows that various types of inappropriate personal protective equipment were used by workers. Nineteen percent (19%) of the workers don’t use any PPE. Active ingredients absorption through the skin is the most common cause of pesticide poisoning and may occur during mixing, loading and spraying. Wearing appropriate PPE will minimize exposure.

The examination of obtained result shows that the poisoning symptoms are not function to professional qualification. Nevertheless, it was see that the most affected workers are drivers and phytosanitary brigades. Many studies showed that the most agents involved in pesticides mixing, loading and spraying are phytosanitary brigades. Their exposure could be the result of inadequate protection.

With regard to cholinesterase monitoring, 67% of workers had cholinesterase inhibition after active ingredients handling. This inhibition could be associated with the effects of organophosphorus pesticides. By inhibiting acetylcholinesterase, these organophosphorus or carbamates pesticides allow acetylcholine to accumulate and result in initial excessive stimulation followed by depression.

According to threshold action of World Health Organization (WHO), fifteen percent of surveyed workers had an inhibition rate between 20 and 30%, which is an exposure alert. supervisors must evaluate the workplace and correct any unsafe practices. Thirty-four percent (34%) of workers had an inhibition rate between 30 and 50%. This inhibition rate suggests possible health effects. The workers need temporarily stop working with pesticides. Finally, 23% of workers had an inhibition rate higher than 50%. This inhibition corresponds to a sign of poisoning. The principal workers must stop temporarily working with pesticides and need medical assistance.

From the results of the model, it was observed for the two scenarios that during mixing, loading and spraying without personal protective equipment, operators involved in locust control in Niger are exposed more to dimethoate, chlorpyrifos and cyhalothrin than other insecticides. Dimethoate and chlorpyrifos are organophosphates which are very toxic and can stimulate cholinesterase inhibition in humans. From the above results, it was also observed that with regard to the spraying method, the exposure of workers using a hand-held sprayer was higher than the exposure of workers using a vehicle mounted sprayer for all active substances. The exposure levels exceed several times higher the acceptable operator exposure level (AOEL taken as reference). Operators are faced with significant risk in using all active substances when no personal protective equipment is used.However, this significant risk of exposure was greatly reduced when operators wear appropriate personal protective equipment.

5. CONCLUSION:

In summary, the results of this study show that workers involved in locust control in Niger had attitudes and practices to increase exposure to plant protection products formulations. In fact, the most results of this study combining acetylcholinesterase monitoring and model exposure evaluationshow that the exposure levels are well correlated with acetylcholinesterase inhibition. In all cases, it appears that workers involved inNiger locust control are faced with significant risks. Therefore, there is an important need to assess pesticides potential risksboth on populations and environment.

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Received on 22.11.2017 Modified on 25.01.2018

Research J. Science and Tech. 2018; 10(1):40-51

DOI: 10.5958/2349-2988.2018.00006.2