Health monitoring : Arsenic (inorganic)

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

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

In the marine environment, inorganic arsenic is taken up by fish, shellfish and algae (including seaweed) and is stored as organic arsenical compounds. These compounds are considered non-toxic. Arsenobetaine is the major species of organic arsenic in fish. In contrast, arsenosugars are the major species of organic arsenic in seaweed.   

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

Inorganic arsenic binds to red blood cells and is deposited in the liver, kidneys, muscle, bone, hair, skin and nails. Arsenic also readily crosses the placental barrier and can potentially result in adverse effects on the foetus.

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

Inorganic arsenic is rapidly excreted via the kidneys, of which 10-20 per cent is excreted unchanged, 10-20 per cent as MMAv and 60-80 per cent as DMAv.

Excretion commences within the first few hours after exposure. Most of the arsenic is excreted in the urine within three days (with a 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, as well as individual characteristics and health status.

Arsenic is a local irritant to mucous membranes and causes eye irritation, nose irritation, epistaxis and nasal septum perforation.

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.

Skin folds (nose, mouth, axillae, scrotum) with moist surfaces are susceptible to local irritation, vesiculitis, folliculitis and ulcers. Arsenic also causes skin hyperpigmentation, hyperkeratosis and sensitisation. The skin changes are the most obvious signs of chronic inorganic arsenic toxicity.

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

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

Health monitoring

Health monitoring consists of:

• taking a medical and work exposure history,as well as a smoking and vaping history
• conducting a clinical examination of the skin (hands, forearms and exposed areas), as well as the respiratory and peripheral nervous systems
• biological monitoring (urinary arsenic).

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

• checking for other sources of arsenic (for example, seafood, arsenical products, smoking)
• informing workers of potential adverse health effects from arsenic dust or fumes
• counselling all workers to stop smoking
• encouraging workers to be clean shaven for effective respiratory protection when using respiratory protective equipment
• ensuring workers understand safety controls in the work environment
• reinforcing safe work practice, particularly the use of appropriate personal protective equipment and respiratory protective equipment
• reinforcing personal hygiene and cleanliness, including:
  • washing of the face and hands before eating, drinking or smoking
  • not eating, drinking or smoking in locations where arsenic is present
  • showering and changing into clean clothes and footwear before leaving the work area.

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 (DMAv and MMAv) is the preferred method for biological monitoring (inorganic arsenic).

Urinary total arsenic analysis includes contributions from dietary (organic) sources of arsenic.  If total urinary arsenic (non-speciated) analysis is used and the levels exceed 35 µg/L, the registered medical practitioner should instruct the pathology laboratory to automatically perform speciation.

Biological exposure standard for inorganic arsenic

• Urinary inorganic arsenic (As(III) + As(V) and MMAv + DMAv) 35 µg/L

Consumption of seafood contributes to the level of urinary arsenic. Arsenobetaine in fish and shellfish is excreted unchanged in urine. Some molluscs also contain DMAv. Arsenosugars in seaweed are metabolised to DMAv. This can affect the results of urinary inorganic arsenic analysis.

Tobacco smokers may have slightly higher levels of urinary arsenic. This is due to the presence of arsenic in cigarettes, which in turn creates a potentially reduced capacity for the elimination of arsenic.

Timing

• The worker must abstain from consuming seafood and seaweed (including fish sauce, shrimp paste and sushi) for at least four days prior to testing.
• The worker must shower prior to providing a sample. This is to avoid contamination by their skin and clothing.
• For chronic exposure, urine samples should be collected at the end of the shift, at the end of the work week. This is generally after four to five days of working with arsenic. 

Frequency

• New workers should be tested within a month of starting arsenic-risk work.
• The frequency of testing depends on the trends shown by recent biological monitoring and air monitoring results for the similar exposed group (SEG) of workers attesting to the effectiveness (or otherwise) of workplace controls.
• Biological exceedances indicate the need for workplace investigation and remedial measures, and hence more frequent testing.
• An initial minimum of three-monthly testing is recommended. However, for specific high risk scenarios, such as gold rooms (pouring gold) or baghouse (filtering dust containing arsenic) the frequency and timing of testing will need to be adjusted to be representative of the exposure and tasks performed. Maintenance contractors with intermittent exposure will have a different frequency of testing in contrast with an employee with regular exposure.
• The registered medical practitioner in consultation with the PCBU can make adjustments (especially reduction in frequency) by considering the effectiveness of workplace controls and recent trends demonstrated by biological monitoring and air monitoring results.

Contractors

• Contractors who perform arsenic-risk work on a site are required to comply with the same biological monitoring requirements as employees.
• Newly appointed contractors, who have previously worked in an arsenic-risk work environment, must be tested for urinary arsenic before starting work. The exception to this is if an acceptable recent urinary arsenic exposure level is available. To determine if it is safe for the contractor to commence work, the test should be undertaken at least two days before they are due to start work.

The registered medical practitioner determines whether the worker may or may not continue working with arsenic.

The registered medical practitioner also:

• 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.

Removal of workers

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.
• In the event, a serious skin, lung or neurological condition has been identified and assessed as likely to be related to arsenic exposure, it is recommended that the worker be removed from arsenic-risk work with a prompt referral to an appropriate medical specialist to confirm the diagnosis and to advise on clinical management. A copy of the medical specialist’s report is to be made available to WorkSafe. In determining whether the worker can safely resume work in an arsenic-risk work environment, the registered medical practitioner should consider the adequacy of workplace controls, as well as advice from the medical specialist.

The registered medical practitioner must complete the WorkSafe Health monitoring form notification: Other

The registered medical practitioner must then notify WorkSafe by forwarding reports and test results to safety@demirs.wa.gov.au