Regulators in Western Australia are considering proposals for two new chemical plants on the Burrup peninsula that would increase air pollution near the world’s largest collection of rock art.

The news comes three months after the WA government announced it was preparing to nominate the site for a world heritage listing, for the 1m petroglyphs throughout the area and its surrounding islands, some of which are more than 60,000 years old.

It also follows a Senate report that warned emissions from heavy industry on the peninsula could damage the carvings, prompting rock art experts to call for a halt to new industry approvals until both the baseline emissions figures and an accurate picture of the damage being done to the images could be established.

The Perdaman urea project, which proposes to manufacture 2m tonnes of the compound used in fertiliser each year on a site adjacent to the Murujuga national park, and the Wesfarmers downstream processing chemical production facility, which would manufacture 5,000 tonnes of methanol a day on nearby land, were this month referred to a public environmental review by WA’s Environmental Protection Authority.

The EPA also ordered a public environment review on a proposal by Woodside to extend to 2070 the operation of the North-West Shelf gas project, which has been operating on the Burrup peninsula for more than 30 years.

All three projects raised potential damage to the rock art caused by increased emissions as a risk in their applications for environmental approval. They also highlighted the absence of any accepted baseline data on both the level of emissions on the peninsula and the damage of airborne emissions to the petroglyphs.

WA’s environment minister, Stephen Dawson, said the environmental assessment process would consider the potential impact of the proposals on the rock art, using information provided by the proponents about “their estimated baseline air emissions”.

“In addition, the Department of Water and Environmental Regulation is currently in the process of establishing an ambient (background) air quality monitoring network covering the Burrup peninsula airshed,” he said.

But he did not say whether the government would require the EPA’s environment review to wait until the baseline emissions data was available.

Dawson said the EPA would be required to consider the potential impact of the proposals on the rock art, but could not consider the potential economic or social impacts of approving any proposal that may impact upon a future world heritage nomination.

The Perdaman urea project is proposed for sites C and F of the Burrup strategic industrial area, an area of zoned industrial land that is surrounded by the Murujuga national park. The sites are on either side of Hearson Cove Road and run along Burrup Road, which runs to the gas plant.

The rock art is concentrated within the national park, which is jointly managed with the Murujuga Aboriginal Corporation (MAC), but petroglyphs are scattered throughout the industrial estate.

Site E, the proposed site of the Wesfarmers chemical plant, has been identified as particularly sensitive by MAC. Until 2013 it housed a compound of rock art that had been cleared by Woodside in the early 1980s to make way for the gas plant. MAC’s chief executive, Peter Jeffries, told Guardian Australia in August that people should be “careful” about building a new plant in an area that was already “badly disturbed”.

MAC has been advocating for all new industrial development to be placed on the Maitland industrial estate, 30km away.

The former Australian Greens leader Christine Milne has accused the WA government of deliberately delaying the world heritage nomination process to allow time for further industrial development on the Burrup.

“It is appalling that the government of WA is fully aware that the acid levels on the petroglyphs have increased, and that this will destroy them over time, and yet continue to prioritise industrial growth and government revenue over protection of Aboriginal culture and world heritage,” Milne said in a letter last month to the Australian Heritage Council.

Dawson said the WA government was not deliberately delaying the process but was working with MAC and the federal government to prepare a tentative list submission for consideration by the Unesco world heritage committee.

“The federal government have indicated that they cannot progress world heritage nominations while they are members of the Unesco committee, of which they are members of until 2021, so 2022 is the earliest that the nomination can be agreed to,” he said.