Hawaii residents returning to neighborhoods devastated by streams of molten rock from the Kilauea volcano have new threats to worry about – acid rain and volcanic smog, according to a new report.

Authorities have warned that dangerous levels of sulfur dioxide gas could spew out of cracks left in the ground by the ongoing eruption in the Leilani Estates and Lanipuna Gardens neighborhoods, CNN reported.

When sulfur dioxide and other gases emitted from the volcano react with oxygen, moisture and sunlight they produce volcanic smog — known as vog — and acid rain.

High chances of rain on the Big Island Thursday make these phenomena all the more likely, CNN meteorologist Michael Guy said.

The acid rain would damage plants and metal objects such as cars, buildings and industrial and farm equipment. In a worst-case scenario, it could also contaminate rooftop rainwater-catchment systems — which residents use for drinking water — with lead, according to the US Geological Survey.

Volcanic smog, a kind of hazy air pollution, could also be caused by the sulfur dioxide gas.

Infants, the elderly and those who suffer from respiratory conditions and cardiovascular disease would be especially vulnerable to vog. At higher concentrations, it can also cause headaches and irritation to the lungs and eyes.

“For people with asthma and other respiratory problems, the effects are much more serious, causing a tightening of the airways in the lungs and making it very difficult to breathe,” the University of Hawaii at Hilo said.

But there has been no clear evidence that vog would harm normally healthy individuals.

More than two dozen homes and buildings have been destroyed and about 2,000 people forced to evacuate because of the eruption.

So acid rain and volcanic smog are “really about the least of their worries,” said University of Hawaii meteorologist Steven Businger.