I suppose it would depend upon an exact definition of ‘disaster’, but the Romans could have quite a major impact on local ecology. The first thing that came to my mind was the extensive gold mines in what is now north-western Spain. One, Las Medulas, is a UNESCO World Heritage Site today. If you Google images of Las Medulas you can get an idea of what the Romans did to the landscape there.

The Romans used hydraulic mining in places, undermining a mountain with immense quantities of water. They used so much water, in fact, that the water table was impacted more than at any period, including even today.

They had to deforest the area, and this combined with the hydraulic mining resulted in an entire transformation of the local landscape. Studies of pollen taken from peat cores have shown a pretty significant change in the local ecology.

Also, studies of ice cores from Greenland clearly show the effects of Roman metallurgy. This does not necessarily constitute a ‘disaster,’ I think, but it does show the high level of metalworking taking place in the Roman era and it probably suggests more drastic local effects, like to the people living closest to high concentrations of metal forges.

In Spain, metal pollution at the La Molina peat mire was higher than at any period before the late modern period. The mineral content spiked at the end of the late Roman period and was even higher than it is today.

Now I don’t know of any proof of increased human sickness or death due to this activity. There is an old idea that the Romans managed to poison themselves with lead (particularly due to lead pipes) but this has been frequently challenged. We also know that the Romans knew the dangers of lead, because Vitruvius writes about it, so I suspect the idea of mass lead poisoning is somewhat overstated. Yet I would be surprised if those working in or living close to these mines did not have some adverse health problems.

Main source: Lopez-Merino and others; Reconstructing the impact of human activities in NW Iberian Roman mining landscape for the last 2500 years ; Journal of Archaeological Science; 2014