The most serious environmental effect posed by hazardous wastes is ?

Groundwater contamination is the most common and serious environmental effect of hazardous wastes. Historically, hazardous wastes have been disposed of in regular landfills that resulted in unfavorable amounts of hazardous materials seeping into the ground. These chemicals eventually entered natural hydrologic systems. Many landfills now require countermeasures such as phytoremediation against groundwater contamination.