6.2 Routes of Exposure, Symptoms, and Cholinesterase

40 CFR 171.103(c)(2)(iii) and (vii) require commercial applicators to recognize likely ways dermal, inhalation, and oral exposure occur and to know symptoms of pesticide poisoning. National Core adds ocular (eye) contact as a fourth route because the eye is both a local-injury target and a rapid absorption surface. Oklahoma work makes those four routes concrete: a Category 1 agricultural loader at a wheat-country nurse tank, a turf technician walking a still-wet fairway, a 7A technician cracking a crack-and-crevice aerosol in a restaurant dish room, a ROW crew treating guardrail vegetation from an open ATV, or a fumigator at a grain bin.

Four routes, four typical job stories

Dermal exposure is contact with skin. National Core is direct: in most cases the skin is the main route of pesticide entry onto or into the body, and some studies show that up to 97 percent of all body exposure to pesticides during a spraying operation is by skin contact. That 97 percent figure is a National Core citation about spraying operations, not a claim that every Oklahoma task is 97 percent dermal, and it is not a made-up "90 percent" rule. Hands and forearms take a large share of handler contact; National Core's PPE chapter notes research in which workers mixing pesticides received about 85 percent of total exposure on the hands and 13 percent on the forearms, and wearing protective gloves cut that exposure dramatically. Dermal contact happens when you splash while measuring an EC, brush a wet boom, adjust a leaking nozzle with a bare hand, pull contaminated gloves off with your teeth, wear the same coverall into the pickup, or reenter turf, wheat stubble, or a treated ROW before the deposit has dried. Residue on ATV grips, steering wheels, cell phones, and cab door handles continues the exposure after the spray job looks finished.

Absorption is not uniform. Oklahoma State University's pesticide toxicity fact sheet, reproducing the comparison used throughout National Core teaching, sets the forearm at 1.0 and notes that the lower groin absorbs more than eleven times as fast—fast enough to approach the effect of putting the material into the bloodstream. Sweat, heat, and abraded skin increase uptake. A soaked pant cuff at the boot line during a July sod job is not a small event just because the product was a turf herbicide rather than an insecticide. Absorption continues for as long as the residue stays on the skin, so time-to-wash is part of the dose.

Inhalation is breathing vapor, aerosol, or dust. It is the dominant concern with fumigants in grain bins and structures, with fine dusts and wettable powders in a closed shed, with fogging or misting in a 7A account, and with any application in still air inside a restaurant, greenhouse, or enclosed trailer. Smoking with contaminated fingers, burning empty bags, mixing indoors without ventilation, and wearing a poorly sealed respirator all create inhalation dose. A closed spray cab reduces drift on the skin, but a dusty hopper fill, a cab filter that is overdue, or an opened window during an inversion can still put airborne material into the breathing zone.

Oral exposure at work is almost always hand-to-mouth, not a decision to drink the tank mix: eating, dipping a chew, vaping, or drinking from a bottle handled with residue on the cap. Splashes into the mouth while pouring, blowing out a nozzle, or siphoning by mouth (never acceptable) are acute oral events. Away from the job, unlabeled containers remain the classic high-dose oral pathway for children and for anyone who grabs the wrong bottle in a shop refrigerator.

Ocular exposure is a splash, mist, or rubbed residue in the eye. Dry formulations in wind, boom drip at face height, and removing goggles with contaminated gloves are routine causes. The eye can be damaged locally (especially by DANGER products with irreversible eye effects) and can also absorb enough material to contribute to systemic poisoning.

Acute symptoms depend on chemical class

40 CFR 171.103(c)(2)(vii) expects symptom recognition, not a guess that every insecticide in Oklahoma still works like parathion. Oklahoma Extension notes that since the late 1990s many insecticide uses shifted from organophosphate (OP) and carbamate products toward pyrethroids. You will still see cholinesterase inhibitors on some agricultural, public-health, and specialty labels; you will also see herbicides, fungicides, rodenticides, and growth regulators whose acute picture looks nothing like OP poisoning. Read the label and SDS for the product in the tank.

Organophosphate and carbamate insecticides inhibit cholinesterase, the enzyme that lets nerves reset after signaling with acetylcholine. When the enzyme is blocked, secretions and smooth-muscle activity run unchecked. Training mnemonics such as SLUDGE (salivation, lacrimation, urination, diarrhea, gastrointestinal upset, emesis) and DUMBBELS (diarrhea, urination, miosis, bradycardia/bronchospasm, emesis, lacrimation, salivation) describe that cholinergic pattern. National Core groups milder findings (fatigue, headache, dizziness, blurred vision, sweating, salivation, nausea, cramps, diarrhea) separately from moderate findings (weakness, chest discomfort, pinpoint pupils) and severe findings (twitching, pulmonary secretions, coma). Pinpoint pupils, heavy secretions, and muscle twitching are useful clues when an OP or carbamate was actually used. They are not a description of glyphosate, a phenoxy herbicide, or a typical pyrethroid turf product.

Pyrethroids more often produce local paresthesia—burning, tingling, or prickling on exposed skin—and, if swallowed in a serious dose, neurologic effects that can include seizures, especially in small children. That is a different first-aid and medical picture than cholinesterase inhibition.

Herbicides, fungicides, and many 7A residuals may present as irritation, headache, or nausea without a textbook SLUDGE cluster. Fumigants can cause cough, chest tightness, dizziness, or sudden collapse from inhalation; treat them as inhalation emergencies, not as "just a smell." Anticoagulant rodenticides are a delayed bleeding problem after ingestion, not an immediate cholinergic crisis.

Local (contact) injury happens at the skin or eye. Systemic injury happens after the chemical is absorbed. Either can be an emergency. National Core also separates allergic responses from ordinary irritation: hives, blistering dermatitis, asthma, or shock can appear after a product that others on the crew tolerate.

Chronic endpoints: label and SDS, not rumor

Repeated exposure concerns—cancer, reproductive effects, endocrine disruption—are evaluated in registration and, when EPA requires communication, appear as label precautionary language and SDS toxicology sections. Do not build a chronic-risk story from a social-media list of "bad chemicals," and do not ignore a statement that is actually on the documents in the truck. If a product carries a chronic hazard statement, driving exposure toward zero is the professional response: closed systems, the labeled PPE, hygiene, and keeping bystanders and children out. If you need medical advice after repeated handling of an OP or carbamate, that is also a cholinesterase-monitoring conversation, not a guess.

Cholinesterase monitoring is medical, not a blanket Oklahoma statute

National Core teaches that cholinesterase monitoring can be appropriate for people who handle organophosphate and carbamate insecticides. The useful protocol is a baseline blood test while you are not exposed, then periodic tests compared with that baseline, plus a test if you feel ill. A significant drop supports a diagnosis of overexposure; medical professionals commonly keep the person away from further OP/carbamate exposure until levels recover—National Core mentions on the order of three to five weeks for rebuilding enzyme, which is a medical timeline, not a DIY schedule.

Oklahoma does not impose a general ODAFF rule that every certified applicator, including a 7A technician using only pyrethroids or a ROW applicator using only herbicides, must file annual cholinesterase bloodwork. Monitoring is driven by the product label, by an employer's medical surveillance program (including Worker Protection Standard medical-evaluation pieces for respirators, which are not the same test), and by a clinician's judgment after a suspected OP/carbamate incident. Pyrethroids, phenoxy herbicides such as 2,4-D, and most turf fungicides are not cholinesterase-monitoring products. Do not skip PPE because you had a blood test, and do not skip a needed test because "Oklahoma never requires it" if the label or your medical program does.