Confusion is mounting over the environmental credentials of Apple's portfolio after research from the US Electronic Product Environmental Assessment Tool (EPEAT) appeared to contradict recent claims from Greenpeace that the company's products are some of the most environmentally damaging on the market.

The EPEAT research, which is backed by the federal Environmental Protection Agency (EPA), instead ranked some of Apple's products amongst the most environmentally friendly available, granting relatively high rankings to several of its notebooks, desktops and monitors.

The EPEAT ranking system gauges products based on 23 mandatory criteria and 28 optional criteria covering areas such as the product's energy efficiency, take back scheme, ease of recycling and use of hazardous components and chemicals.

Firms have to achieve all mandatory criteria to gain a bronze ranking, a further 50 percent of the optional criteria to gain a silver ranking, and all the mandatory criteria and over three quarters of the optional criteria to be awarded a gold ranking.

While none of the assessed firms achieved a gold ranking, Apple was amongst the best performers achieving a silver ranking for all its assessed products, including its Mac Pro, MacBook Pro and Cinema HD monitor.

The research prompted several reports highlighting the apparent discrepancy  between the two ranking systems' conclusions and led to plenty of gloating from Mac enthusiasts who have long claimed Greenpeace produced bias research in order to target Apple and exploit the company's high profile.

However, Scot Case, marketing director at EPEAT, insisted there was no contradiction between the two ranking systems' findings and that neither could be used to prove the inaccuracy of the other. "My initial reaction was that comparing the two systems was like comparing apples and oranges, but on closer inspection it is more like comparing apples and cows," he said. "EPEAT focuses on ranking the products, Greenpeace is looking at the whole company."

Greenpeace agreed Apple's contrasting position in the two ranking systems could be explained by their different criteria. "If both reports used the same criteria and had such different rankings then one report would have to be bogus," said Iza Kruszewska, toxics campaigner for Greenpeace International. "But we are using very different criteria."

According to Kruszewska, the criteria used in Greenpeace's own report were narrower in focus, only looking at the chemicals used in the products and the manufacturers' eWaste policies, but more stringent in these areas compared to EPEAT.

"For example, one of the mandatory criteria for EPEAT is compliance with the RoHS directive," she explained. "But we don't give companies credit for that as compliance with RoHS is something they should be doing across the board as a minimum."

Similarly, one of the mandatory EPEAT criteria states that "all flat panel video display devices manufacturers shall report on the amount of mercury used in light sources in all covered products". But Kruszewska said that Greenpeace's system required firms to "ban Mercury, not report on it", in order to gain a high ranking.

Another difference is found in the two ranking systems' attitudes to PVC and brominated flame retardants. Whereas EPEAT states that ensuring large plastic parts are free of PVC and hazardous flame retardants is an optional criteria - one which the 16 ranked Apple products admittedly met - Greenpeace wants firms to commit to eliminating PVC and brominated flame retardants from the whole product and publish a timeline for achieving their elimination.

"We've got commitments from many manufacturers to be free of these chemicals by 2009 or 2010, but Apple has not given us any such commitment," said Kruszewska. "These chemicals are toxic and they are persistent within the environment."

Greenpeace also marked down Apple in its report for failing to clearly define the precautionary principle it follows in material selection and refusing to provide more detailed information about the substances used in its products.

The protest group further argued that Apple would not even qualify for the EPEAT bronze ranking if the criteria were applied globally as it does not operate a take-back scheme – mandatory under EPEAT's ranking system - in every region that the company operates.

However, Case rejected suggestions that the EPEAT standards were not stringent enough, noting that no product had yet achieved the higher gold standard ranking. "What EPEAT is trying to do is create market-based incentives for companies to improve the environmental standards of their products," he said. "We're educating corporate purchasers to buy EPEAT approved products and that has created an incentive for manufacturers to move towards achieving the gold ranking."

Apple said in a statement that it disagrees with Greenpeace's rating and the criteria it chose. "Apple has a strong environmental track record and has led the industry in restricting and banning toxic substances such as mercury, cadmium and hexavalent chromium, as well as many BFRs (brominated flame retardants)," the statement read. "We have also completely eliminated CRT monitors, which contain lead, from our product line."

But Kruszewska insisted Apple was falling behind in the race to improve the environmental sustainability of IT products. "Between the first and second edition of our report other companies - including some of the Asian players who are operating in far less stringent regulatory environments - have made substantial improvements to their environmental policies," she said. "But Apple has done very little."

She added that Apple's resistance appeared to be at least partly a result of their secretive corporate culture. "They don't like to be pushed and have told us that they don't give commitments about future products - they just get on and do it. Well if that's the case we wish they would just hurry up [and release greener products]," she said. "They are design leaders and we expect them to do far better."