The 2012 Olympics could fall short of its environmental pledges, the London Assembly has warned.
London 2012 pledged the Games will be the most sustainable in recent history.
But the Going for Green report said a lack of electric vehicles, air pollution and renewable electricity targets were areas of concern.
The report praised London's 2012's approach to mapping its carbon footprint and its aim to reuse or recycle 90% of temporary materials.
Organisers should be applauded for their green pledges but "we don't want to see environmental standards compromised" in the run-up to the Games, Darren Johnson, chairman of the London Assembly's Environment Committee said.
Not securing more electric vehicles for the Olympic fleet was a "missed opportunity", the committee's report found.
It is still not clear how carbon emissions from travel to London will be reduced and a target on renewable electricity during the staging phase of the Games is unlikely to be met, it states.
London's air quality, which has also not improved as hoped since 2005, is also said to be a "particular concern".
Forecasts suggest there will be harmful levels of the pollutant nitrogen dioxide (NO2) in crucial parts of London in 2012, the committee said.
Mr Johnson said: "London's air quality is a particular cause for concern, as failing to reduce levels of pollutants could have consequences for London's international reputation as well as the health of those attending the event.
"We also need to see clear targets for re-using temporary materials, more detail on how organisers will promote sustainable travel and plans for recycling facilities on site and around London."
A London 2012 spokesperson said: "LOCOG welcomes the report published today from the assembly, which credits the work undertaken by all the stakeholders to ensure that London 2012 is the most sustainable Games possible.
"The Commission for a Sustainable London 2012 is the independent body set up to ensure this, and LOCOG works closely with them on all aspects of our work."