9.4 Chemical Families, Signs & Symptoms of Poisoning
Key Takeaways
- A symptom is what the affected person reports; a sign is what an observer can see or measure.
- Organophosphates and carbamates inhibit acetylcholinesterase, producing the cholinergic toxidrome summarised by SLUDGEM and DUMBELS.
- Carbamate inhibition of cholinesterase is reversible and spontaneously reactivates, while organophosphate inhibition can become irreversible through ageing.
- Pyrethroids act on voltage-gated sodium channels and typically cause paraesthesia, tingling and burning of exposed skin.
- Anticoagulant rodenticides inhibit vitamin K epoxide reductase, blocking synthesis of clotting factors II, VII, IX and X and causing internal haemorrhage.
Chemical Families, Signs & Symptoms of Poisoning
Why this matters: "Signs and symptoms" is a named leaf of Domain 3. Recognising a poisoning pattern in the field means knowing which chemical family you are working with and what its toxidrome looks like — starting with the cholinergic picture organophosphates and carbamates produce.
1. Major Pesticide Chemical Families & Toxicodynamics
Different pesticide chemical classes exert distinct biochemical mechanisms of action on human physiological systems. Certified applicators must understand these mechanisms to recognize poisoning syndromes and communicate effectively with attending emergency physicians.
┌────────────────────────────────────────────────────────────────────────┐
│ MAJOR PESTICIDE CLASSES & MODES OF ACTION │
│ │
│ 1. ORGANOPHOSPHATES (OPs): │
│ • Irreversible covalent phosphorylation of Acetylcholinesterase. │
│ • Causes massive acetylcholine accumulation at synapses. │
│ • Undergoes "aging" (irreversible permanent bond formation). │
│ │
│ 2. CARBAMATES: │
│ • Reversible carbamylation of Acetylcholinesterase active site. │
│ • Spontaneous enzyme regeneration occurs within hours. │
│ • CRITICAL: 2-PAM antidote is strictly contraindicated! │
│ │
│ 3. SYNTHETIC PYRETHROIDS: │
│ • Axonal voltage-gated sodium channel modulators (prolong opening).│
│ • Causes nerve membrane depolarization and paresthesia. │
│ │
│ 4. BIPYRIDYLIUMS (Paraquat / Diquat): │
│ • Intracellular redox cycling generating reactive oxygen radicals. │
│ • Paraquat selectively concentrates in lung pneumocytes → fibrosis.│
│ │
│ 5. ANTICOAGULANT RODENTICIDES: │
│ • Inhibit Vitamin K Epoxide Reductase (VKOR). │
│ • Halts clotting factor synthesis (II, VII, IX, X) → hemorrhage. │
│ │
│ 6. FUMIGANTS (Phosphine, Metam Sodium): │
│ • Cytochrome c oxidase inhibition (cellular suffocation). │
│ • Acute pulmonary edema, cardiovascular collapse, tissue necrosis. │
└────────────────────────────────────────────────────────────────────────┘
Detailed Toxicological Profiles of Major Chemical Families
| Chemical Family | Representative Active Ingredients | Biochemical Mode of Action | Key Human Signs, Symptoms & Diagnostic Indicators |
| :--- | :--- | :--- | :--- |
| Organophosphates (OPs) | Chlorpyrifos, malathion, diazinon, dimethoate, acephate, phosmet | Irreversible inhibition of Acetylcholinesterase (AChE) via phosphorylation of catalytic serine. Causes hyperaccumulation of acetylcholine (ACh) at muscarinic, nicotinic, and CNS receptors. Undergoes enzyme "aging." | Cholinergic toxidrome (SLUDGEM / DUMBELS): Pinpoint pupils (miosis), excessive salivation, profuse sweating, bronchospasm, frothy sputum, muscle twitching (fasciculations), seizures, coma. |
| Carbamates | Carbaryl (Sevin®), methomyl (Lannate®), oxamyl (Vydate®), formetanate | Reversible carbamylation of Acetylcholinesterase (AChE). Enzyme spontaneously hydrolyzes and regenerates within 24 to 48 hours. | Identical cholinergic symptoms to OPs, but shorter clinical duration. 2-PAM is contraindicated because carbamate-enzyme complex resolves spontaneously and 2-PAM increases carbamate toxicity. |
| Synthetic Pyrethroids | Permethrin, bifenthrin, cypermethrin, lambda-cyhalothrin, deltamethrin | Modulate axonal voltage-gated sodium ($Na^+$) channels, delaying channel closure and causing prolonged depolarizing after-potentials and repetitive nerve discharge. | Cutaneous paresthesia (intense facial burning, tingling, or numbness upon skin contact). Type II pyrethroids (with cyano group) cause choreoathetosis, salivation, tremors, and seizures. |
| Bipyridylium Herbicides | Paraquat dichloride, diquat dibromide | Intracellular redox cycling: Accepts electrons from NADPH and transfers them to molecular oxygen, generating lethal surges of superoxide free radicals ($O_2^{\bullet-}$) and hydrogen peroxide, inducing widespread lipid peroxidation. | Paraquat concentrates selectively in alveolar type I and II pneumocytes, causing destructive alveolitis followed by fatal progressive pulmonary fibrosis (lung scarring). Supplemental high-flow oxygen worsens toxicity. |
| Anticoagulant Rodenticides (SGARs & FGARs) | Brodifacoum, bromadiolone, difethialone (SGARs); Warfarin, diphacinone (FGARs) | Competitive inhibition of Vitamin K Epoxide Reductase (VKOR), blocking the cyclic regeneration of active Vitamin $K_1$, halting the post-translational carboxylation of clotting factors II (prothrombin), VII, IX, and X. | Massive spontaneous internal hemorrhage, hematuria, epistaxis (nosebleeds), bleeding gums, widespread ecchymoses (bruising), abdominal pain, hypovolemic shock. Elevated prothrombin time (PT/INR). |
| Chlorophenoxy Herbicides | 2,4-D, MCPA, triclopyr, dicamba | Uncoupling of oxidative phosphorylation and disruption of cellular membrane transport; central nervous system and skeletal muscle toxicity. | Severe nausea, vomiting, burning epigastric pain, muscle fasciculations, profound muscle weakness, myotonia, metabolic acidosis, rhabdomyolysis. |
| Fumigants (Phosphine & MITC Generators) | Aluminum phosphide (releases $PH_3$), metam sodium / dazomet (releases MITC) | Phosphine inhibits mitochondrial Cytochrome c Oxidase, halting ATP synthesis and inducing catastrophic cellular anoxia and free radical production. MITC causes direct mucous membrane destruction. | Phosphine: Sudden pulmonary edema, acute respiratory distress syndrome (ARDS), refractory cardiovascular shock, cardiac arrhythmias, multi-organ failure. Odor of decaying fish or garlic. |
What is the primary biochemical mechanism of toxicity in human poisonings caused by second-generation anticoagulant rodenticides (SGARs) such as brodifacoum?
2. Signs vs. Symptoms & Poisoning Severity Assessment
In medical toxicology and field emergency assessment, clinical indicators are divided into two distinct categories:
┌────────────────────────────────────────────────────────────────────────┐
│ SIGNS VS. SYMPTOMS OF POISONING │
│ │
│ 1. SYMPTOMS (Subjective - Felt by the Victim): │
│ • Physical sensations experienced and reported by the patient. │
│ • Cannot be directly seen or measured by an external observer. │
│ • Examples: Nausea, frontal headache, dizziness, blurred vision, │
│ metallic taste in mouth, abdominal cramps, chest tightness, │
│ numbness, tingling paresthesia, profound fatigue. │
│ │
│ 2. SIGNS (Objective - Observed by Others): │
│ • Physical, measurable, visible evidence of physiological trauma. │
│ • Can be detected by co-workers, first responders, or physicians. │
│ • Examples: Pinpoint pupils (miosis), vomiting (emesis), profuse │
│ sweating (diaphoresis), excessive drooling (salivation), │
│ muscle twitching (fasciculations), staggering gait (ataxia), │
│ cyanosis (bluish skin), convulsions, unconsciousness. │
└────────────────────────────────────────────────────────────────────────┘
Stages of Acute Poisoning Severity
Pesticide toxicosis progresses across three clinical severity tiers depending on chemical potency, absorption rate, and total absorbed dose:
| Severity Level | Characteristic Symptoms (Reported by Patient) | Characteristic Signs (Observed by Co-workers / Rescuers) | Immediate Operational Actions Required |
| :--- | :--- | :--- | :--- |
| Mild Poisoning | Mild frontal headache, fatigue, dizziness, lightheadedness, mild nausea, loss of appetite, irritation of nose and throat. | Slight perspiration, bloodshot eyes, mild restlessness, slight pupil constriction. | Immediately cease all pesticide handling. Remove from application zone to fresh air. Decontaminate skin/clothing. Monitor continuously for 24 hours. |
| Moderate Poisoning | Severe throbbing headache, blurred or dark vision, continuous nausea, abdominal cramping, extreme weakness, chest tightness, mental confusion. | Profuse sweating, excessive salivation (drooling), vomiting, diarrhea, visible muscle twitching (fasciculations) in eyelids/tongue, constricted pinpoint pupils, unsteady staggering gait. | Call 911 immediately. Transport to emergency medical facility with product label and SDS. Perform complete skin decontamination en route. Administer oxygen if trained. |
| Severe Poisoning | Inability to breathe, extreme chest constriction, visual blackout, intense abdominal agony, feeling of impending doom. | Copious frothy pulmonary secretions, severe respiratory distress / wheezing (bronchorrhea), pinpoint non-reactive pupils, generalized muscle twitches, clonic-tonic convulsions, loss of bowel/bladder control, coma, respiratory arrest. | Call 911 / ALS dispatch immediately. Initiate immediate CPR / rescue breathing with barrier device if breathing stops. Immediate aggressive hospital antidote therapy (Atropine + 2-PAM). |
3. The Cholinergic Toxidrome: SLUDGEM & DUMBELS
Poisonings involving Organophosphates (OPs) and N-methyl Carbamates inhibit acetylcholinesterase, producing hyperstimulation of the parasympathetic nervous system, sympathetic ganglia, neuromuscular junctions, and central nervous system. Emergency responders and toxicologists utilize standardized clinical mnemonics to recognize this cholinergic toxidrome:
┌────────────────────────────────────────────────────────────────────────┐
│ THE CHOLINERGIC TOXIDROME MNEMONICS │
│ │
│ S ── Salivation (Drooling) D ── Diarrhea │
│ L ── Lacrimation (Tears) U ── Urination (Incontinence) │
│ U ── Urination (Incontinence) M ── Miosis (Pinpoint Pupils) │
│ D ── Defecation (Diarrhea) B ── Bradycardia & │
│ G ── Gastrointestinal Cramps Bronchorrhea/Bronchospasm│
│ E ── Emesis (Vomiting) E ── Emesis (Vomiting) │
│ M ── Miosis (Pinpoint Pupils) L ── Lacrimation (Tears) │
│ S ── Salivation (Drooling) │
└────────────────────────────────────────────────────────────────────────┘
Anatomical Receptor Breakdown of Cholinergic Symptoms
- Muscarinic Effects (Parasympathetic Postganglionic Hyperstimulation):
- Exocrine Glands: Profuse sweating (diaphoresis), excessive tear production (lacrimation), copious watery drooling (salivation), and rhinorrhea (runny nose).
- Respiratory Tree: Massive hypersecretion of watery mucus in bronchial airways (bronchorrhea) combined with severe airway constriction (bronchospasm)—often termed "liquid drowning in one's own secretions."
- Cardiovascular: Profound slowing of heart rate (bradycardia, heart rate $<50\text{ bpm}$) and hypotension.
- Gastrointestinal & Ocular: Severe hyperperistalsis causing agonizing abdominal cramps, vomiting, involuntary defecation/urination, and severe pupillary constriction (pinpoint miosis).
- Nicotinic Effects (Sympathetic Ganglia & Neuromuscular Junctions):
- Skeletal Muscle: Initial fine, involuntary twitching and flickering of muscle bundles (fasciculations), particularly visible in the eyelids, tongue, facial muscles, and calves.
- Motor Exhaustion: Progresses to profound muscle weakness, loss of deep tendon reflexes, and flaccid paralysis of the diaphragm and intercostal muscles, culminating in acute ventilatory failure.
- Central Nervous System (CNS) Effects:
- Restlessness, agitation, anxiety, cognitive confusion, slurred speech, ataxia, generalized clonic-tonic convulsions, coma, and central depression of the brainstem respiratory drive.
An applicator assisting a coworker who collapsed in an orchard notices that the victim is drooling heavily, sweating profusely, has wet rattling breathing sounds, and exhibits pinpoint pupils (miosis). What do these clinical findings indicate?