exposure to organophosphate & carbamate insecticides monitoring for over exposure

Exposure to Organophosphate & Carbamate Insecticides

Monitoring for Over Exposure

Principles of Monitoring

Detect organophosphate [OP] or carbamate [Carb] exposures before employees get sick

Based on OP/Carb inhibitory effects of the enzyme- cholinesterase

OPs effects are long term - “irreversible” Carbs effects are shorter term -

“reversible”

Mechanism of Action

Inhibits Cholinesterase– enzyme responsible for

hydrolyzing acetylcholine to choline

– choline reabsorbed and acetylated ( + = )

Enzyme inhibition leads to excess accumulation of acetylcholine at nerve synapse or neuromuscular receptor

Nerve Ending

Neuromuscular Junction

Health Effects from Overexposure

Cholinergic stimulation– SST: salivation, sweating, tearing– blurred vision (miosis)– nausea/vomiting, abdominal pains,

diarrhea– chest tightness, wheezing

Nicotinic stimulation– muscle twitching, tremors– weakness– anxiety, irritability

How is Biological Monitoring Possible? Presence of cholinesterase enzymes in

RBCs and Plasma– reflect what may be happening in nervous

system and muscles Lab methodologies prevalent “Simple” blood test (but it’s not too

simple)

Factors for Adequate Monitoring

Great variability between individuals & within the same individual

Use two unexposed specimens to average baseline (1-2 weeks apart)

Generally ignore Laboratory “Normal Range”– Individual serves as own baseline b/o great variability

Using same lab, same methodology Cooling down specimens quickly & expeditious

processing– inhibition of enzymes can be reversible, esp. Carbs,

resulting in false negatives

Plasma vs. RBC Cholinesterase

Plasma Cholinesterase– aka serum, pseudo- or

butyrylcholinesterase

– quick fall and quick recovery after exposure

– 0.03-3.0% genetic deficiency in population

• False “low” reading• can cause panic• not at > risk from

exposure however

RBC Cholinesterase– aka acetylcholinesterase

– slower to fall and recover post-exposure

– no known genetic deficiency

– good for non-acute exposure monitoring

Using Cholinesterase Activity to Assess Toxicity

Correlation between depression of activity and health effects

At > 25% inhibition, occurrence of adverse effects rises quickly - “slippery slope”

Does employee have potential for exposure to organophosphates (OP) or carbamates (CARB)?

No Yes Don't Know

Obtain Safety / Industrial Hygiene input before proceeding. See partial list of

commonly used OPs and CARBs (attached)

Stop! Establish Baseline Levels:• Before job assignment or reassignment

to job with potential for exposure• In lieu of this, make sure employee is

free from potential exposure for > 4 weeks

• Obtain first set of RBC and Plasma Cholinesterase levels

• Approximately one week later, obtain second set of RBC and Plasma Cholinesterase levels

• Average both sets – this establishes employees baseline.

• Baseline data should be readily available to employee and supervisory personnel in the event of an acute exposure.

Does employee have potential for exposure to organophosphates (OP) or carbamates (CARB)?

NoYes

Stop!

Cholinesterase Biological Monitoring for OP/Carb Exposure

Clinical Component Safety/ Industrial Hygiene Component

Monitor Periodically:• Frequency Dependent Upon Exposure (for

example)• Pesticide Applicators – monthly• Seasonally, Biannually or Annually for others• Assessment requires Safety input• For most instances, RBC cholinesterase levels

only need to be obtained• Exceptions: Phosdrin (mevinphos); chlorpyrifos:

require plasma cholinesterase levels

Drop in cholinesterase levels > 25% baseline?

YesNo

Continue monitoring • Remove from Exposure• Notify Safety / IH Office• Repeat levels in 1-2

weeks, under guidance of Occupational Medicine Professional

• Return to duties once employee recovers and Doctor/Safety deems okay.

Notify Safety / IH office to investigate work site and assess potential for excessive exposure

Cholinesterase Biological Monitoring for OP/Carb Exposure

Clinical Component Safety/ Industrial Hygiene Component

ACUTE EXPOSURE INCIDENT OCCURS:Spill, Leak, Breakdown in Engineering, Personal Protective

Equipment, or other sudden event which leads to unequivocal employee exposure

Does employee have any symptoms or did employee require any decontamination

procedures (shower, partial wash, eye wash, etc.)? [See below for list of symptoms of acute

exposure]

Yes to either No to each

Transport immediately toEmergency/Urgent Care Center:• Evaluation by health

professional• Draw RBC and Plasma

cholinesterase levels• Treatment as needed

Counsel employee to seek medical attention immediately if any symptoms develop (review symptoms with employee)

Arrange for testing for RBC and Plasma cholinesterase levels within 24 hours

Conclusions

Establish adequate baselines– RBC and Plasma Levels

Identify genetically “low” plasma cholinesterase levels

Use similar lab/methodologies Process and Cool Specimen quickly

Conclusions (cont’d)

Look for >25% Depression– only when employee works with

organophosphate or carbamate insecticides

– use RBC only, with notable exceptions (mevinphos; chlorpyrifos)

Check plasma cholinesterase under acute exposure circumstances