Arsenic is widely distributed in rocks and soil. Arsenic is highly toxic in its inorganic form.

Occupational exposure to arsenic occurs in mining and refining processes including roasting arsenopyrite ore and smelting minerals such as gold, lead, zinc and copper. Arsenic is present in mining waste. Arsenic exposure also occurs in industries such as waste disposal, some manufacturing and laboratories. It is used, or has historically been used, in metal alloys, pigments, ceramic enamels, anti-fouling paints, pesticides, rat poison, and leather hide and wood preservation.

Fish, shellfish and seaweed contain arsenobetaine and arsenosugars. These sources of organic arsenic are referred to as dietary arsenic and are not considered toxic.

Inorganic arsenic enters the body by inhalation or ingestion. The respiratory tract is the major portal of entry in occupational exposure. Arsenic compounds such as arsenic trioxide are soluble in bodily fluids and cleared rapidly from the lungs. Less soluble arsenic compounds (calcium arsenate, lead arsenate, arsenic sulphide) are retained in the lungs and 80-90% of arsenic trioxide is absorbed by the gastrointestinal tract. Dermal absorption is likely to be low.

Inorganic arsenic binds to red blood cells and is deposited in liver, kidneys, muscle, bone, hair, skin and nails. Arsenic readily crosses the placental barrier with potential for adverse effect on the foetus.

Arsenic is metabolised by the reduction of pentavalent arsenic (As(V)) to trivalent arsenic (As(III)), and methylation to metabolites (monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)). Trivalent arsenic is more toxic than pentavalent arsenic. Methylation is triggered after about eight hours.

Inorganic arsenic is rapidly excreted via the kidneys, of which 10-20% is excreted unchanged, 10-20% as MMA and 60-80% as DMA.

Excretion commences within the first few hours after exposure. Most of the arsenic is excreted in the urine within three days (half-life of one to two days). However, it may take weeks to completely eliminate a single dose.

Symptoms from exposure vary depending on the dose, chemical form, mode and duration of exposure, individual characteristics and health status.

Acute poisoning results in acute abdominal pain, nausea, vomiting, diarrhoea, cramps in the extremities, restlessness and spasms. There may be cardiac arrhythmias, liver toxicity, kidney failure and peripheral neuropathy, convulsions, dehydration, shock and death at very high doses.

Arsenic is a local irritant to mucous membranes resulting in eye irritation, nose irritation, epistaxis and even nasal septum perforation. Skin folds (nose, mouth, axillae, scrotum) where surfaces are moist, are susceptible to local irritation, vesiculitis, folliculitis and ulcers. Arsenic also causes skin hyperpigmentation, hyperkeratosis and sensitisation. The skin changes are the most specific obvious signs of chronic inorganic arsenic toxicity.

Chronic poisoning may cause peripheral neuropathy, cardiomyopathy and arrythmias, and non-malignant pulmonary changes.

Inorganic arsenic is classified as a carcinogen (Group 1, IARC) in humans. The metabolites, MMA and DMA, are classified as possible carcinogens (Group 2B, IARC). Chronic arsenic exposure is associated with skin, lung and bladder cancer. Skin cancers include basal cell carcinoma and squamous cell carcinoma. Smoking has been shown to increase the risk of lung cancer in exposed workers.

Health monitoring should be undertaken annually together with health counselling.

Health monitoring consists of:

• a medical and work exposure history
• examination of the skin (hands, forearms and exposed areas), lungs and peripheral nervous system
• biological monitoring (urinary arsenic).

The registered medical practitioner has an important role in educating and reinforcing good personal hygiene and safe work practices.

• Check for other sources of arsenic (e.g. seafood, arsenical products, etc.).
• Inform workers of potential adverse health effects from arsenic dust or fumes.
• Counsel all workers to stop smoking.
• Be clean shaven for effective respiratory protection when using respiratory protective equipment (RPE).
• Understand safety controls in the work environment.
• Reinforce safe work practice, particularly the use of appropriate personal protective equipment (PPE) and respiratory protective equipment (RPE).
• Reinforce personal hygiene and cleanliness, including:
  • washing face and hands before eating, drinking or smoking
  • no eating, drinking or smoking in the workshop or room where arsenic is present
  • showering and changing into clean clothes and footwear before leaving the work area.

• Urinary inorganic arsenic by speciation (As(III) plus As(V) plus metabolites, MMA and DMA) should not exceed 35 µg/L.

• Urine samples should be collected and tested at the end of the shift on the last day of the work week. The worker needs to shower prior to providing a sample to avoid contamination by skin or clothing. The worker should also abstain from consuming seafood and seaweed for at least three days prior to providing a sample.

• New workers should have initial testing for urinary arsenic and again at 1 month
• Workers in arsenic-risk work should have urinary arsenic testing according to their test results as per Table 1.
• Workers with intermittent arsenic exposure, e.g.  weekly gold pour in gold rooms, should have a urinary arsenic level at least two days prior to the pour, and again four days after the pour.  Should two consecutive sets of test results be satisfactory, the frequency of sampling may be reduced to accordingly as per Table 1.
• Contractors who perform arsenic-risk work on a site are required to comply with the same biological monitoring requirements as for employees. 
• Any contractor who is new to a work site, but had previously  been working in an arsenic-risk work environment, must be tested for urinary arsenic prior to starting work.  It is recommended that the test be undertaken at least two days before starting so that the results are available beforehand.   This will determine if they are safe to start. 

Arsenic levels in urine are indicative of exposure over the previous two to three days. Measurement of inorganic As(III), As(V) and the metabolites (DMA and MMA) is the preferred method for biological monitoring.

If the biological method used is total urinary arsenic (non-speciated) and the levels exceed 35 µg/L, the pathology laboratory should be instructed to automatically perform speciation.

Avoidance of seafood and seaweed for three days prior to urine sampling is essential because dietary arsenic compounds may be substantial. Seafood and seaweed contain organic arsenic compounds including arsenobetaine and arsenosugars. Arsenobetaine is excreted rapidly unchanged in urine. However, DMA is a major metabolite of arsenosugars (found in seaweed).

Tobacco smokers may have slightly higher urinary arsenic levels due to the presence of arsenic in cigarettes and a potentially reduced capacity for elimination of arsenic.

Blood testing is not recommended as arsenic is cleared from the blood rapidly and may have poor correlation with recent exposure.

The Registered Medical Practitioner reviews the test results to determine whether the worker may or may not continue working with arsenic.

The Registered Medical Practitioner:

• explains the results of the health monitoring to the worker
• provides feedback to the employer in relation to remedial action (i.e. safety improvements)
• notifies WorkSafe.

When urinary arsenic (inorganic) is 35 µg/L or more, the registered medical practitioner:

• removes the worker from arsenic exposure
• conducts a medical review as soon as can be arranged with emphasis on skin, respiratory system and peripheral nervous system
• requests the PCBU reviews safety controls, systems of work, personal hygiene and personal protective equipment
• repeat urinary arsenic level in 2 weeks
• recommends a return to arsenic work when urinary arsenic (inorganic) is 20 µg/L or less and there are no other clinical concerns.

However, when a serious skin, lung or neurological condition has been identified and assessed as  likely to be related to arsenic exposure, removal from arsenic-risk work is recommended.  A prompt referral to an appropriate medical specialist to confirm the diagnosis and advise on clinical management.  A copy of the medical specialist report is to be made available to WorkSafe.  The registered medical practitioner should take into consideration the advice from the medical specialist advice and adequacy of workplace controls in determining whether the worker may safely resume work in an environment which potentially exposes them to arsenic.

The Registered Medical Practitioner notifies WorkSafe at DMIRS by forwarding reports and test results to safety@dmirs.wa.gov.au.