Growing so large that they are now called “factory farms,” livestock feedlots are poorly regulated, pose health and ecological dangers, and are responsible for a deteriorating quality of life in America’s and Europe’s farm regions, according to a series of studies published this week by scientists.

Animal feedlots are contaminating water supplies with pathogens and chemicals, and polluting the air with foul-smelling compounds that can cause respiratory problems, but the health of their neighbors goes largely unmonitored, the reports concluded.

The international teams of environmental scientists also warned that the livestock operations are contributing to the rise of antibiotic-resistant germs, and the proximity of poultry and hogs could hasten the spread of avian flu to humans.

Feedlots are operations where hundreds, often thousands, of cattle, hogs, dairy cows or poultry are confined often in very close quarters. About 15,500 medium-to-large livestock feedlots operate in the United States, and it is roughly an $80 billion-a-year industry.