Hazards Associated with Aerial Spraying of Organophosphate Insecticides in Israel M. Gordon1 and E.D. Richter2 1
Occupational Medical Unit Hadassah Hospital, and 2 Unit of Occupational and Environmental Medicine Hebrew University - Hadassah Medical School Jerusalem, Israel
ABSTRACT
Aerial application of organophosphates can result in exposure to drift and leaf residues for pilots, ground crews, field workers, and residents near sprayed fields. Exposure can be by either the airborne or dermal route, and can produce illness (headaches, fatigue, diarrhea, cramps, respiratory problems) even with low-grade depressions in Cholinesterase. Alkyl phosphate metabolites have been shown to be "gold standard" measures of such exposures. Experience in Israel indicates that reduction of health hazards from exposure to drift and leaf residues may be attained by the use of a comprehensive "mix" of preventive measures. These measures include, first and foremost, reduction in total amount of organophosphates used, followed by substitution of less for more toxic organophosphates, reduction in length of spray season, banning the use of flaggers, and greater reliance on tractor spraying. Cotton yield per hectare cultivated has increased despite a reduction in use of pesticides of all kinds and organophosphates in particular. Enclosure and air-conditioning (to prevent heat stress) of cockpits, protective clothing, training and licensing of pilots have been implemented. Education and communication of information, in keeping with the right-to know principle on hazards and how they should be controlled and monitored, is a part of a comprehensive strategy. Aerial or Reprint address: Dr. Milton Gordon Occupational Medical Unit Hadassah Hospital, Ein Karem Jerusalem, Israel
ground spraying should produce no drift in adjacent residential communities. The criterion for achieving this goal is the absence of urine alkyl phosphate metabolites above the threshold of detection. INTRODUCTION
The intentional misuse of anticholinesterases for mass killing in the Iran-Iraq war, and threats by Iraq to use similar measures in the Gulf War, have emphasized the potent effects and extreme potential public health hazards from these highly toxic agents. Unintentional exposure may occur in humans when anti-cholinesterases are used for pest control and crop protection. This paper reviews the protective measures in Israel when exposure occurs by drift and residues from aerial spraying. Aerial spraying is carried out wherever there is a need for rapid application of pesticides to large or remote land areas /l/. Considering the quantities applied, aerial spraying of pesticides has produced a relatively low reported number of acute work intoxications. In California, for example, aerial spray workers over the years have applied some 60% of all the pesticides used. However, they represented only 10% of the total reported pesticide illness episodes /2/. This low reported incidence is a consequence of the low worker/ pesticide tonnage ratio. On the other hand, aerial spraying results in dispersion or drift over greater areas than ground spraying /3/. The economic advantages and relative safety of aerial spraying have been offset by the hazards and
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Μ. GORDON AND E.D. RICHTER
risks for specific population sub-groups, especially pilots, for whom the risks are crash injury and death from neuro-behavioral effects of low level exposures /4-10/. For ground crew workers, the risks occur from direct contact associated with transportation, preparation, mixing, formulating, loading and disposal of the pesticides and equipment maintenance, while for field workers, pickers, and leaf inspectors, there are risks from direct contact with residues when working in sprayed fields. In addition, there is the potential for community exposure to pesticide drift when aerial spraying is carried out near residential areas / l l , 12/. For all groups, preventive measures must be taken, based on an assessment of the sources and pathways of exposure 191. In Israel, aerial application of pesticides to fields adjacent to residential communities has already been shown to result in community exposure, as evidenced by the appearance of alkyl phosphate metabolites in the urine of residents /13/. In the early 1980s in Israel, about one million hectares (2.5 million acres) were treated by aerial application every year. EXPOSURE TO SPRAY DRIFT OF PESTICIDES
Droplets of pesticide agents between 50-100 μ diameter can impact on the nasal lining and be absorbed transmucosally; droplets smaller than 50 μ can penetrate the upper respiratory tract, and droplets of 1-10 μ can impact on the smallest bronchioles. Much smaller droplets, 0.1 μ, pass through the whole respiratory tract and are exhaled. The downwind drift of sprays is 4 to 5 times higher than that produced by high clearance ground sprayers. Dry dusts produce more downwind drift than wet sprays prepared as water emulsions or wettable powders. This is why modern pesticide aerial application has been in the form of sprays instead of dry dusts /3/. Drift from cropdusting is much greater than drift from crop-spraying. With aerial drift spraying, small droplets are released at high altitude which remain suspended for longer periods. Drift spraying has been used against airborne pests such as the tsetse fly, locusts or for "covering" large areas of forest. The slow descent of the aerial drift spray means longer ae-
rial residence time - an advantage when the target is an airborne pest. Ultra-low volume (ULV) aerial drift application in Israel has been limited to the control of the Medfly by a combination of malathion and a protein hydrolysate bait in citrus and deciduous orchards. With placement spraying, larger drops are released from low altitudes in narrow swaths. The goal is to deliver pesticides to the plant surface HI. For drift spraying, aircraft are equipped with rotary atomizers for ULV drift application. A boom and nozzle are used for placement spraying for conventional applications. ULV sprays are potentially more toxic per unit mass because they disperse highly concentrated preparations of pesticide. Although they require a lower total volume per unit area, the greater downwind drift may produce very high exposure and absorption. WORK CONDITIONS OF PILOTS AND GROUND CREW INVOLVED IN AERIAL SPRAYING
Over the years, the work schedule of pilots involved in aerial spraying in Israel has usually included early hours, 4-5 hours flight time, 10-15 take-offs and landings per day, passes at 2-3 meters above ground, several hundred 180 degree turns or flying in box patterns following short runs of several hundred meters (with possible re-exposure to the spray), frequent passes under power lines, and exposure to heat, noise, vibration and gravitational forces 111. Our previous papers have reported hazards due to exposure to organophosphates /5,7/ and heat stress /8,14/, and crash risk 161 produced by the work conditions /6-8,14/. For the ground crew workers, absorption of pesticides has been shown to occur mainly via the dermal route 15/. Compared to pilots, these workers are at greater risk for overt intoxication and Cholinesterase depression, especially in the vicinity of aircraft washdowns. In the past, these workers, because they have developed tolerance to the muscarinic warning effects of pesticides, tended to consider themselves resistant to the neuro-toxic effects of these agents. Educational efforts have been necessary to dispel these dangerous misconceptions.
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AERIAL SPRAYING OF ORGANOPHOSPHATES
EVIDENCE OF EXPOSURE TO AIRBORNE PESTICIDES
Biological monitoring Today, studies in several countries indicate that the absolute proof of exposure to organophosphates (OPs) and their absorption is provided when alkyl phosphate metabolites are detected in the urine of symptomatic or asymptomatic individuals/15-18/. These metabolites are excreted in the urine immediately following exposure and are reported to disappear within 48 to 72 hours following termination of exposure /16, 19-22/. The traditional evidence of specific biologic effect at the receptor site is when plasma, red blood cell or whole blood Cholinesterase is found to be substantially lowered compared to the person's own baseline, which sometimes has to be determined retroactively, or, less satisfactorily, compared to Cholinesterase levels of unexposed persons/15,23, 24/. Certain OPs may have other effects on the nerves independent of lowered Cholinesterase activity and prior to the neuro-muscular junction, e.g. at the neurotoxic esterase receptor site on the neuronal myelin sheath or, as it has been renamed, neuropathy target esterase (ΝΤΕ). Estimation of Cholinesterase activity depression may not necessarily detect these effects /19/. Alkyl phosphates and Cholinesterase activity provide complementary types of information. Occurrence of alkyl phosphates in urine indicates immediate or recent OP exposure (within the last 24-48 hours). Changes in Cholinesterase activity reveal current and cumulative effects of recent exposure. Recovery of Cholinesterase activity occurs following termination of exposure /23,25/. There are suggestions that alkyl phosphate metabolites in the urine may appear following exposures that produce symptoms (e.g. headaches, fatigue, abdominal cramps, diarrhea, breathing problems) even when Cholinesterase is near "normal" or very slightly depressed (e.g. < 20%) /26/. The follow up of such metabolites in urine, therefor, may be better for surveillance of populations, for periodic checks at low levels of exposure and for the evaluation of the efficiency of exposure control measures, such as re-entry time standards for field personnel entering sprayed fields /27,28/.
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231
Assays of alkyl phosphate metabolites in urine can also be used to detect exposure to OPs producing effects other than those associated with inhibition of Cholinesterase, e.g. impairment of peripheral sensory function from NTE-type actions. Low level toxic effects, involving the peripheral nerves, were suggested in a study carried out on kibbutz residents in Israel who had frequent complaints of numbness and tingling. These complaints were associated with slight in-season drops of peak action potential amplitudes — a measure of axon impairment in both the sural and peroneal nerves (Table 1). Environmental monitoring Air sampling, using personal and stationary samplers, together with dermal patches, has been well described elsewhere, /3, 5, 7/; their use is to help trace sources and pathways of exposure. Bee colony mortality has been known to be a sensitive indicator of drift exposure to organophosphates or other pesticides including chlorinated hydrocarbons /30/. Bee colony mortality, therefore, could serve as a low cost, easy to use environmental biologic sentinel for drift exposure of residential populations. The same has been reported to be true for fish species in waterways and open reservoirs /31/. The use of now available Cholinesterase impregnated paper markers to detect drift should also be considered. As a general rule, where outdoor temperatures are high, toxic intermediate oxidation products (e.g. parathion breaking down to paraoxon) may be more readily produced from pesticide drift settling on leaf surfaces, and therefore longer lasting residues can be expected. In addition, higher temperatures can be expected to result in more evaporation of settled spray on leaf surfaces, and therefore higher ambient concentrations of both precursors and intermediates 1321. PREVENTIVE ACTIONS
Measures to reduce exposure The general principles of preventive action to reduce exposure to airborne insecticides include the following:
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Μ. GORDON AND E D . RICHTER
TABLE 1 Electromyogram examinations of peripheral nerves of 12 kibbutz workers and 5 kibbutz residents exposed to parathion, chlorpyritos and diazinon Pre-season (ti) and in-season (t2); Israel 1984 SD
Mean Peroneal nerve Distal Latency (ms a )
Residual Latency (ms a )
b
Conduction Velocity (m/s )
c
Amplitude (mv )
Sural Nerve Latency to onset (ms a )
Latency to peak (ms a )
Conduction Velocity (m/sb)
Conduction Velocity Peak
(m/sb)
Amplitude (mv°)
ti t2 ti-t2 ti t2 tl-t 2 tl t2 tl-t2 tl t2 tl-t2
4.17 4.01 -0.16 2.91 2.71 -0.20 57.11 55.12 -2.01 12.73 10.62 -2.12
1.15 1.09 0.90 1.27 1.22 0.99 11.98 10.86 6.49 4.55 4.24 4.95
tl t2 tl-t2 tl t2 tl-t2 tl t2 tl-t2 tl
2.89 2.95 + 0.06 3.61 3.64 + 0.04 43.32 43.78 +0.46 53.04
0.20 0.16 0.20 0.20 0.23 0.90 1.66 2.10 2.02 2.94
t2 tl-t2 tl t2 tl-t 2
52.98 -0.05 21.97 18.83 -3.14
2.73 3.25 13.42 5.87 14.92
Ρ Two tailed
%Change (mean)
0.47
+ 3.8
0.42
+ 6.7
0.22
+3.5
0.10
-16.6
0.23
+2.0
0.49
+ 1.0
035
+ 1.0
0.94
+ 0.9
0.20
-143
a
ms = milliseconds m/s = meters/second c mv = milivolts Source: Richter et al., 1988 /29/ b
TABLE 2 Urinary alkyl phosphate metabolites (DMP and DEP) of kibbutz residents vs distance from fields sprayed with parathion (Israel, 1987)a Metabolite Distance (m) 100-499 500-1000
nb 6 5
DMP (mg/1)
Occupational Medical Unit Hadassah Hospital, and 2 Unit of Occupational and Environmental Medicine Hebrew University - Hadassah Medical School Jerusalem, Israel
ABSTRACT
Aerial application of organophosphates can result in exposure to drift and leaf residues for pilots, ground crews, field workers, and residents near sprayed fields. Exposure can be by either the airborne or dermal route, and can produce illness (headaches, fatigue, diarrhea, cramps, respiratory problems) even with low-grade depressions in Cholinesterase. Alkyl phosphate metabolites have been shown to be "gold standard" measures of such exposures. Experience in Israel indicates that reduction of health hazards from exposure to drift and leaf residues may be attained by the use of a comprehensive "mix" of preventive measures. These measures include, first and foremost, reduction in total amount of organophosphates used, followed by substitution of less for more toxic organophosphates, reduction in length of spray season, banning the use of flaggers, and greater reliance on tractor spraying. Cotton yield per hectare cultivated has increased despite a reduction in use of pesticides of all kinds and organophosphates in particular. Enclosure and air-conditioning (to prevent heat stress) of cockpits, protective clothing, training and licensing of pilots have been implemented. Education and communication of information, in keeping with the right-to know principle on hazards and how they should be controlled and monitored, is a part of a comprehensive strategy. Aerial or Reprint address: Dr. Milton Gordon Occupational Medical Unit Hadassah Hospital, Ein Karem Jerusalem, Israel
ground spraying should produce no drift in adjacent residential communities. The criterion for achieving this goal is the absence of urine alkyl phosphate metabolites above the threshold of detection. INTRODUCTION
The intentional misuse of anticholinesterases for mass killing in the Iran-Iraq war, and threats by Iraq to use similar measures in the Gulf War, have emphasized the potent effects and extreme potential public health hazards from these highly toxic agents. Unintentional exposure may occur in humans when anti-cholinesterases are used for pest control and crop protection. This paper reviews the protective measures in Israel when exposure occurs by drift and residues from aerial spraying. Aerial spraying is carried out wherever there is a need for rapid application of pesticides to large or remote land areas /l/. Considering the quantities applied, aerial spraying of pesticides has produced a relatively low reported number of acute work intoxications. In California, for example, aerial spray workers over the years have applied some 60% of all the pesticides used. However, they represented only 10% of the total reported pesticide illness episodes /2/. This low reported incidence is a consequence of the low worker/ pesticide tonnage ratio. On the other hand, aerial spraying results in dispersion or drift over greater areas than ground spraying /3/. The economic advantages and relative safety of aerial spraying have been offset by the hazards and
VOLUME 9, NO. 4,1991
229 Brought to you by | University of Arizona Authenticated Download Date | 5/31/15 3:00 AM
230
Μ. GORDON AND E.D. RICHTER
risks for specific population sub-groups, especially pilots, for whom the risks are crash injury and death from neuro-behavioral effects of low level exposures /4-10/. For ground crew workers, the risks occur from direct contact associated with transportation, preparation, mixing, formulating, loading and disposal of the pesticides and equipment maintenance, while for field workers, pickers, and leaf inspectors, there are risks from direct contact with residues when working in sprayed fields. In addition, there is the potential for community exposure to pesticide drift when aerial spraying is carried out near residential areas / l l , 12/. For all groups, preventive measures must be taken, based on an assessment of the sources and pathways of exposure 191. In Israel, aerial application of pesticides to fields adjacent to residential communities has already been shown to result in community exposure, as evidenced by the appearance of alkyl phosphate metabolites in the urine of residents /13/. In the early 1980s in Israel, about one million hectares (2.5 million acres) were treated by aerial application every year. EXPOSURE TO SPRAY DRIFT OF PESTICIDES
Droplets of pesticide agents between 50-100 μ diameter can impact on the nasal lining and be absorbed transmucosally; droplets smaller than 50 μ can penetrate the upper respiratory tract, and droplets of 1-10 μ can impact on the smallest bronchioles. Much smaller droplets, 0.1 μ, pass through the whole respiratory tract and are exhaled. The downwind drift of sprays is 4 to 5 times higher than that produced by high clearance ground sprayers. Dry dusts produce more downwind drift than wet sprays prepared as water emulsions or wettable powders. This is why modern pesticide aerial application has been in the form of sprays instead of dry dusts /3/. Drift from cropdusting is much greater than drift from crop-spraying. With aerial drift spraying, small droplets are released at high altitude which remain suspended for longer periods. Drift spraying has been used against airborne pests such as the tsetse fly, locusts or for "covering" large areas of forest. The slow descent of the aerial drift spray means longer ae-
rial residence time - an advantage when the target is an airborne pest. Ultra-low volume (ULV) aerial drift application in Israel has been limited to the control of the Medfly by a combination of malathion and a protein hydrolysate bait in citrus and deciduous orchards. With placement spraying, larger drops are released from low altitudes in narrow swaths. The goal is to deliver pesticides to the plant surface HI. For drift spraying, aircraft are equipped with rotary atomizers for ULV drift application. A boom and nozzle are used for placement spraying for conventional applications. ULV sprays are potentially more toxic per unit mass because they disperse highly concentrated preparations of pesticide. Although they require a lower total volume per unit area, the greater downwind drift may produce very high exposure and absorption. WORK CONDITIONS OF PILOTS AND GROUND CREW INVOLVED IN AERIAL SPRAYING
Over the years, the work schedule of pilots involved in aerial spraying in Israel has usually included early hours, 4-5 hours flight time, 10-15 take-offs and landings per day, passes at 2-3 meters above ground, several hundred 180 degree turns or flying in box patterns following short runs of several hundred meters (with possible re-exposure to the spray), frequent passes under power lines, and exposure to heat, noise, vibration and gravitational forces 111. Our previous papers have reported hazards due to exposure to organophosphates /5,7/ and heat stress /8,14/, and crash risk 161 produced by the work conditions /6-8,14/. For the ground crew workers, absorption of pesticides has been shown to occur mainly via the dermal route 15/. Compared to pilots, these workers are at greater risk for overt intoxication and Cholinesterase depression, especially in the vicinity of aircraft washdowns. In the past, these workers, because they have developed tolerance to the muscarinic warning effects of pesticides, tended to consider themselves resistant to the neuro-toxic effects of these agents. Educational efforts have been necessary to dispel these dangerous misconceptions.
Brought to you by | University of Arizona Authenticated REVIEWS ON ENVIRONMENTAL HEALTH Download Date | 5/31/15 3:00 AM
AERIAL SPRAYING OF ORGANOPHOSPHATES
EVIDENCE OF EXPOSURE TO AIRBORNE PESTICIDES
Biological monitoring Today, studies in several countries indicate that the absolute proof of exposure to organophosphates (OPs) and their absorption is provided when alkyl phosphate metabolites are detected in the urine of symptomatic or asymptomatic individuals/15-18/. These metabolites are excreted in the urine immediately following exposure and are reported to disappear within 48 to 72 hours following termination of exposure /16, 19-22/. The traditional evidence of specific biologic effect at the receptor site is when plasma, red blood cell or whole blood Cholinesterase is found to be substantially lowered compared to the person's own baseline, which sometimes has to be determined retroactively, or, less satisfactorily, compared to Cholinesterase levels of unexposed persons/15,23, 24/. Certain OPs may have other effects on the nerves independent of lowered Cholinesterase activity and prior to the neuro-muscular junction, e.g. at the neurotoxic esterase receptor site on the neuronal myelin sheath or, as it has been renamed, neuropathy target esterase (ΝΤΕ). Estimation of Cholinesterase activity depression may not necessarily detect these effects /19/. Alkyl phosphates and Cholinesterase activity provide complementary types of information. Occurrence of alkyl phosphates in urine indicates immediate or recent OP exposure (within the last 24-48 hours). Changes in Cholinesterase activity reveal current and cumulative effects of recent exposure. Recovery of Cholinesterase activity occurs following termination of exposure /23,25/. There are suggestions that alkyl phosphate metabolites in the urine may appear following exposures that produce symptoms (e.g. headaches, fatigue, abdominal cramps, diarrhea, breathing problems) even when Cholinesterase is near "normal" or very slightly depressed (e.g. < 20%) /26/. The follow up of such metabolites in urine, therefor, may be better for surveillance of populations, for periodic checks at low levels of exposure and for the evaluation of the efficiency of exposure control measures, such as re-entry time standards for field personnel entering sprayed fields /27,28/.
VOLUME 9, NO. 4,1991
231
Assays of alkyl phosphate metabolites in urine can also be used to detect exposure to OPs producing effects other than those associated with inhibition of Cholinesterase, e.g. impairment of peripheral sensory function from NTE-type actions. Low level toxic effects, involving the peripheral nerves, were suggested in a study carried out on kibbutz residents in Israel who had frequent complaints of numbness and tingling. These complaints were associated with slight in-season drops of peak action potential amplitudes — a measure of axon impairment in both the sural and peroneal nerves (Table 1). Environmental monitoring Air sampling, using personal and stationary samplers, together with dermal patches, has been well described elsewhere, /3, 5, 7/; their use is to help trace sources and pathways of exposure. Bee colony mortality has been known to be a sensitive indicator of drift exposure to organophosphates or other pesticides including chlorinated hydrocarbons /30/. Bee colony mortality, therefore, could serve as a low cost, easy to use environmental biologic sentinel for drift exposure of residential populations. The same has been reported to be true for fish species in waterways and open reservoirs /31/. The use of now available Cholinesterase impregnated paper markers to detect drift should also be considered. As a general rule, where outdoor temperatures are high, toxic intermediate oxidation products (e.g. parathion breaking down to paraoxon) may be more readily produced from pesticide drift settling on leaf surfaces, and therefore longer lasting residues can be expected. In addition, higher temperatures can be expected to result in more evaporation of settled spray on leaf surfaces, and therefore higher ambient concentrations of both precursors and intermediates 1321. PREVENTIVE ACTIONS
Measures to reduce exposure The general principles of preventive action to reduce exposure to airborne insecticides include the following:
Brought to you by | University of Arizona Authenticated Download Date | 5/31/15 3:00 AM
232
Μ. GORDON AND E D . RICHTER
TABLE 1 Electromyogram examinations of peripheral nerves of 12 kibbutz workers and 5 kibbutz residents exposed to parathion, chlorpyritos and diazinon Pre-season (ti) and in-season (t2); Israel 1984 SD
Mean Peroneal nerve Distal Latency (ms a )
Residual Latency (ms a )
b
Conduction Velocity (m/s )
c
Amplitude (mv )
Sural Nerve Latency to onset (ms a )
Latency to peak (ms a )
Conduction Velocity (m/sb)
Conduction Velocity Peak
(m/sb)
Amplitude (mv°)
ti t2 ti-t2 ti t2 tl-t 2 tl t2 tl-t2 tl t2 tl-t2
4.17 4.01 -0.16 2.91 2.71 -0.20 57.11 55.12 -2.01 12.73 10.62 -2.12
1.15 1.09 0.90 1.27 1.22 0.99 11.98 10.86 6.49 4.55 4.24 4.95
tl t2 tl-t2 tl t2 tl-t2 tl t2 tl-t2 tl
2.89 2.95 + 0.06 3.61 3.64 + 0.04 43.32 43.78 +0.46 53.04
0.20 0.16 0.20 0.20 0.23 0.90 1.66 2.10 2.02 2.94
t2 tl-t2 tl t2 tl-t 2
52.98 -0.05 21.97 18.83 -3.14
2.73 3.25 13.42 5.87 14.92
Ρ Two tailed
%Change (mean)
0.47
+ 3.8
0.42
+ 6.7
0.22
+3.5
0.10
-16.6
0.23
+2.0
0.49
+ 1.0
035
+ 1.0
0.94
+ 0.9
0.20
-143
a
ms = milliseconds m/s = meters/second c mv = milivolts Source: Richter et al., 1988 /29/ b
TABLE 2 Urinary alkyl phosphate metabolites (DMP and DEP) of kibbutz residents vs distance from fields sprayed with parathion (Israel, 1987)a Metabolite Distance (m) 100-499 500-1000
nb 6 5
DMP (mg/1)
