a)Introduction a.1Declaration

a)Introduction

a.1Declaration

Applications for the following AVSRs in use in Australia were received:

• 
  Methylcyclopentadienyl Manganese Tricarbonyl (MMT)-based;
  
• 
  Phosphorous-based;
  
• 
  Sodium-based; and
  
• 
  Potassium-based.
  

a.2Objectives

• 
  Characterise the chemical and physical properties of MMT;
  
• 
  Determine the current and potential occupational, public and environmental exposure to MMT as an AVSR;
  
• 
  Characterise the intrinsic capacity of MMT to cause adverse effects on persons or the environment;
  
• 
  Characterise the risk to humans and the environment resulting from exposure to MMT as an AVSR;
  
• 
  Determine the extent to which any risk is capable of being reduced and make recommendations for the management of these risks.
  

a.3Sources of information

The characterisation of health and environmental risks in Australia was based upon information on use patterns, product specifications, occupational exposure and emissions to the environment made available by the applicant and relevant State and Federal authorities. Information to assist in the assessment was also obtained through site visits and telephone interviews.

a.4Peer review

b)Background

b.1What is an anti-valve seat recession additive?

Although valve seat recession (VSR) occurs as part of the normal wear of an engine, premature erosion of the valve seats observed as excessive VSR occurs when vehicles with soft exhaust valve seats normally designed to operate on leaded petrol are operated on unleaded petrol.

Valve seats in engines designed for leaded fuel are generally relatively soft. With leaded fuels, lead oxide formed by the combustion of lead alkyls forms a thin layer of lead oxide on the valve and valve seat, so acting as a solid lubricant and preventing erosion of the valve seats in the cylinder head of the engine (Figure 1). VSR can cause valve burning and loss of compression and if allowed to progress result in serious loss of performance and ultimately engine failure. Lead replacement petrol uses AVSR additives to provide the lubricating qualities previously provided by lead. During fuel combustion, the AVSR additive burns and forms an oxide coating on the exhaust valve seats providing similar protective lubrication to lead oxide.

Since the early 1970s, increasing environmental and health concerns have resulted in the reduction of lead levels in petrol and the complete removal of leaded gasoline in several countries (Lovei, 1998). In 2000, the World Bank reported that 36 countries had already phased out the use of leaded petrol and this was expected to increase to 55 countries by 2005 (Benbarka, 2000). In addition, the use of catalytic converters in automotive exhaust systems required the introduction of unleaded fuels as lead destroys the capacity of catalytic converters to reduce other pollutants (Lovei, 1998).

A consequence of the removal of lead from petrol is that engine designers have been required to use harder exhaust valve seat materials that maintain integrity without lead lubrication. For existing cars with soft valve seats, the removal of lead has required motorists to use lead replacement petrol containing an AVSR additive or to modify their engine by fitting hardened exhaust valve seats suitable for unleaded petrol with no AVSR fuel additive (Lovei 1998).

The use of AVSR additives has risen with the demand for lead replacement petrol resulting from the lead phase-out worldwide. The demands for lead replacement petrol and hence AVSR additives in individual countries have been determined largely by policy decisions regarding the import, sale and retirement of older vehicles, the encouragement of new technology environmentally cleaner engines and improved petrol standards. Consequently, the population of VSR sensitive cars and thus demand for AVSR additives in lead replacement petrol vary from country to country.