Priority Existing Chemical

m.6Amphibians

m.6.1MMT

m.6.2Manganese

m.7Summary of environmental effects

m.7.1MMT

A predicted no effect concentration (PNEC) for MMT to freshwater organisms of 0.014 mg/L has been derived by applying a standard assessment factor of 10 to the lowest available NOEC data of 0.14 mg/L for freshwater fish (Kem-Tech Laboratories, 1977).

There is currently no environmental hazard classification system in Australia. In accordance with the OECD Globally Harmonized System of Classification and Labelling of Chemicals (OECD 2002), MMT would be classified Chronic 1 Very Toxic to Aquatic Life with Long-lasting Effects.

m.7.2Manganese

Manganese is a naturally occurring element and essential for nutrition in plants and animals. Typical concentrations of Mn in marine and freshwaters approximate 0.003 to 0.38 and 1.5 g/L, respectively (ANZECC and ARMCANZ, 2000).

ANZECC and ARMCANZ (2000) provide a quality guideline (trigger level) for Mn for the protection of freshwater ecosystems of 1.7 mg/L. They calculated this moderate reliability trigger value for Mn using a statistical distribution method with 95% protection and an acute to chronic ratio (ACR) of 9.1. This trigger level is considered to be a suitable predicted no effect concentration (PNEC_Freshwater) for this assessment.

Insufficient toxicity data were available for marine organisms for ANZECC and ARMCANZ (2000) to derive a marine trigger value. They derived a marine interim indicative working level (IIWL) for Mn of 0.8 mg/L. This IIWL was derived by dividing the lowest available acute LC(EC)50 by a standard assessment factor of 20 (Bonnell and Atkinson, 1999, as cited by ANZECC and ARMCANZ, 2000). The lowest acute 48-hour LC50 was 16 mg/L for the American oyster C. virginica (Calabrese et al., 1973, as cited by USEPA, 2000). The value of 0.8 mg/L is considered a suitable PNEC_Marine for this assessment.

The PNEC_Marine and PNEC_Freshwater values are not widely dissimilar in magnitude; however, there is greater uncertainty in the PNEC_Marine than the PNEC_Freshwater due to the lesser amount of marine aquatic toxicity data available (ANZECC and ARMCANZ, 2000).

n)Risk Characterisation

n.1Environmental risk

A hazard quotient (HQ) approach has been used to predict the hazard to terrestrial and aquatic organisms. To predict a low environmental risk, the ratio of PEC to PNEC needs to be 1 or less (i.e. HQ  1).

n.1.1Terrestrial risk

Following combustion, the Mn component in MMT is converted to a mixture of Mn compounds (Mn phosphates, oxides and sulphates), and most will apparently remain in the exhaust train. However, approximately 20% of these Mn compounds may be emitted with exhaust gases associated with very fine particles (< 2.5 μm). These particles have a low quiescent air sedimentation velocity, and may remain suspended in air for a prolonged period. Ultimately, settlement to the earth surface (land and water) will occur, with Mn becoming associated with soils, waters and aquatic sediments.

A predicted no effect concentration (PNEC_mammals) of 6.2 mg/m³ (inhalation) has been derived for mammals exposed to MMT (Section 10.4). Concentrations of MMT in air at a petrol station using MMT in Canada approximated 12 ng/m³ and concentrations were lower in other areas sampled (see Table 5). Given this air MMT concentration at a high use area, and that MMT degrades rapidly when exposed to sunlight, terrestrial wildlife are unlikely to be exposed to MMT in air at levels of concern.

Conservative estimation of potential Mn levels in air indicates an Mn concentration (PEC) of up to 49 ng/m³ (Table 6) for the Present Use scenario. This PEC is several orders of magnitude lower than the conservatively estimated PNEC_mammals of 11.6μg/m³ for Mn in air.

Although no published phytotoxicity data were available on the acceptable concentration of Mn in air for terrestrial plants, no records of adverse effects on plants have been noted in the literature in MMT use areas. The information available indicates that Mn is an essential nutrient for plants and of low toxicity but exposure to high to very high soil Mn concentrations combined with low pH soil conditions, or excessive foliar Mn may lead to adverse effects in plants. However, plants have a propensity to tolerate foliar exposure to Mn and recommended foliar concentrations of Mn typically approximate 1 mg/L, which is several orders of magnitude higher than the estimated concentration of Mn in stormwater in MMT use areas (Section 8.3.4). Aerial deposition of Mn-bound particles onto plants in MMT use areas is unlikely to reach concentrations of concern.

Levels of Mn in soils (using the example of urban runoff in Sydney) are unlikely to reach levels of concern. With the MMT use scenarios developed in Section 8.2, the estimated concentration of Mn deposition from air to land is unlikely to result in unacceptable soil Mn concentrations. In concentration areas such as stormwater, runoff Mn may contain approximately 1.2 μg Mn/L in high MMT use areas (using the Sydney example from Section 8.3.4), several orders of magnitude less than phytotoxicological benchmark for Mn in soil solution of 4 mg/L.

n.1.2Aquatic risk

PNECs for Mn in freshwater and marine waters of 1.7 and 0.8 mg/L, respectively, have been derived (ANZECC and ARMCANZ, 2000; Section 14.5).

As indicated above, the PEC for Mn in stormwater derived from urban runoff may approximate 0.0012 mg/L (refer Section 8.3.4).

Hazard quotients for estimated Mn discharge to freshwater and marine ecosystems from urban runoff have been summarised below:

Predicted Environmental Concentration of Manganese, PEC (mg/L)	Predicted No Effect Concentration for Manganese, PNEC (mg/L)		Hazard Quotient, HQ
0.0012	PNECFreshwater	1.7	HQFreshwater	0.0007
0.0012	PNECMarine	0.8	HQMarine	0.0015