The most significant environmental effect of mining is

Pollution and Land erosion

Explanation:

Mining effects the water lines to clean and maintain a mine. The air gets contaminated with lethal minerals that aren't good for you such as plutonium. Land erosion than occurs when so much land has be excavated from the ground and destabilizeses a foundation in which used to be called a park, a house, or a place to walk on. The land than collapses and causes damage for the locals.