Forensic Toxicology: Metals and Carbon Monoxide

Heavy Metals

One of 23 chemical elements that has a specific gravity (a measure of density) at least five times that of water.

Common toxic metals

Lead (Pb): Paints, old pipes, contaminated soil/water

Mercury (Hg): Fish (bioaccumulation), industrial processes - hat-making

Arsenic (As): Contaminated water, pesticides

Cadmium (Cd): Batteries, cigarette smoke, industrial pollution

Chromium (Cr), Nickel (Ni): Industrial processes, Jewelry

Mechanisms of metal poisoning

cellular disruption, oxidative stress, enzyme inactivation, accumulation

History of metal poisoning

Has been in use since the middle ages - most common was arsenic poisoning.

Symptoms of poisoning

Can include nausea, vomiting, diarrhea, stomach pain, headache, hair loss, sweating, a metallic taste in the mouth.

impaired cognitive, motor and language ability - neurological damage

some are known carcinogens

Why metals are used as poisons

obtainable without rousing suspicions, toxic in small quantities, colorless, tasteless, odorless, can be hidden in food or drink, have delayed onset of action, be undetectable, be chemically stable, and effects should mimic a natural disease.

Chelation therapy

Treatment for most heavy metal poisoning. chelating agents will bind to metals and facilitate excretion from the body. painful and lengthy process.

Common chelating agents

Calcium disodium edetate, dimercaprol (BAL), and penicillamine.

Detecting metals

in blood, urine, hair and tissue analysis using AAS, ICP, x ray imaging.

blood lead levels above 80ug/L

blood mercury levels above 3.6ug/L

urine mecury levels above 15ug/l

arsenic cleared from blood quickly so urine levels over 50ug/l

Atomic Absorption Spectrometry

Measures absorption of light by vaporised atoms.

graphite furnace atomic absorption spectroscopy: uses heated graphite tube to optimise small samples

ICP Techniques

• uses high temperature plasma to excite elements

• the high temperatures prevent interference

• this allows for analyses of a wide range of elements

Carbon Monoxide (CO)

Odourless, colourless and tasteless gas produced as a result of incomplete combustion of organic compounds.

CO sources

• cigarette smoke

• exhaust fumes

• malfunctioning heating and ventilation systems

• fires

CO toxicity mechanism

Carbon monoxide is absorbed into the lungs and rapidly distributes into the blood.

It has a greater affinity to haemoglobin than oxygen.

Haemoglobin takes carbon monoxide around the body instead of oxygen

leading to a shortage of oxygen - anoxia

COHb (%Sat) in non-smokers vs smokers

Ranges from 0 to 3.

3-8 in smokers

Symptoms of acute CO poisoning

Include frontal headache, tremor, nausea, vomiting, blurred vision, seizures, drowsiness, coma, ultimately death.

Postmortem findings for CO poisoning

Cherry pink PM lividity over back indicates suspect CO poisoning.

Treatment of carbon monoxide poisoning

Binding of carbon monoxide to haemoglobin is reversible but it requires the flooding of oxygen. The half life of the carbon monoxide is usually 5 to 6 hours but it is reduced to 30 to 90 minutes in high oxygen environments.

Analysis

• GC for the level of CoHb in blood

10-20% - headache, flushed, shortness of breath

30-40% - weakness nausea confusion

>50% Convulsions, loss of reflexes, respiratory paralysis, death