Priority Existing Chemical

p.4Public health risks

In LRP, MMT is not expected to be a skin irritant at present concentrations. Estimated dermal doses of MMT to be received under a worst case scenario of LRP spillage were several orders of magnitude below comparable animal dermal LD50s. Therefore, there is a low risk of acute health effects for the general public as a result of dermal exposure to MMT in LRP.

Similarly, in aftermarket products, MMT at concentrations presently reported is not expected to be a skin irritant. A comparison of dermal LD50 values with exposure estimates suggests some potential for acute toxicity resulting from dermal exposure to MMT in aftermarket products. However, LD50 values in rats were obtained after a constant 24-hour exposure to MMT and in contrast, much shorter exposures are expected following spillage. Overall, the risk of acute dermal effects in consumers is low given the small amounts of additive to which people are likely to be exposed, the low concentration of MMT present with the fuel additive and that any spill on the skin is unlikely to reside untreated for long periods.

The risk of acute health effects as a result of accidental ocular exposure to MMT in LRP and aftermarket products is also considered to be low since exposure to very small amounts of product is expected to occur only infrequently and MMT is not expected to cause eye irritation at low concentrations present in these products.

Acute health effects could occur as a result of accidental ingestion of MMT by a child or by adults when siphoning fuel. The health risk to adults from accidental ingestion of LRP containing MMT during siphoning or to children following ingestion of LRP stored inappropriately around the home is considered low, given the low level of MMT (< 0.01% w/w) in LRP. However, assuming comparable toxicokinetics of MMT in rats and humans after oral exposure and using the lowest rat LD50 for MMT of approximately 10 mg/kg bw, a child (10kg) ingesting about one mL of an aftermarket product containing 10% w/w MMT could receive a potentially lethal dose. Children between one and a quarter and three and a half years of age can swallow approximately 4.5 mL of liquid, giving a potential dose several times higher than the lowest oral LD50 observed in laboratory animals.

The potential risk associated with accidental ingestion of aftermarket products containing MMT is lessened by the likely storage of aftermarket products in garages, products being generally not “attractive” for ingestion by a child and products as assessed packaged with child resistant closures. However, since very small volumes provide a potentially lethal dose, products containing MMT represent a significant acute health risk for children.

Manganese is a ubiquitous element and chronic Mn exposures (from all sources combined) are unlikely to be significantly changed by the use of MMT. Exposure via food and water forms, by far, the greatest proportion of the total human Mn dose, and are not expected to change significantly as a result of the estimated use of MMT. However, MMT used according to the Present Use scenario of maintained LRP market share or the 2004 scenario of diminished LRP market share will potentially significantly increase the Mn dose received by inhalation (excluding smoking).

Based on the study of Roels et al (1992), the NOAEL for neurological effects in humans was established at 30 μg/m³ and Margins of Exposure were calculated in this report converting intermittent Mn exposures (5 days/week, 24 hours/day) to continuous exposures. For the Present Use scenario, where current LRP market share is maintained with a calculated ambient air concentration for Mn of 4.9 ng/m³, the Margin of Exposure was calculated at 1458. For the 2004 scenario, where the LRP market share declines with a calculated ambient air concentration for Mn of 20 ng/m³, the Margin of Exposure was calculated at 3571. These Margins of Exposure are considered sufficient, taking into account the conservative exposure estimates used.

p.5Data gaps

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  data on potential skin or respiratory sensitisation and effects associated with chronic MMT exposure;
  

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  definitive information on the speciation of Mn compounds emitted during MMT combustion under different driving conditions;
  
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  the toxicokinetics and potential adverse effects of different inorganic Mn compounds resulting from the combustion of MMT;
  
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  health effects associated with chronic, low level Mn exposure, especially in susceptible populations such as children or individuals with compromised liver function; and
  
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  Australian exposure data (personal and ambient air monitoring data) for determining public exposures to Mn especially in environments such as indoors, inside cars, areas of high traffic density and areas with Mn emitting industries.