Land pollution is the result of dumping garbage, waste, and other toxins into soil due to littering, and contaminants washed ashore from boats, oil rigs, and sewage outlets. Another factor contributing to this type of pollution is acid rain. The surface of the Earth is also contaminated by poor agricultural practices, mining, and industrial waste. The excessive waste dumped in landfills or other land sites cleared for new construction causes land pollution as well. Pollutants can remain in the soil for hundreds of years and when new construction is introduced into polluted land, the results on human health can be toxic. If left untreated, contaminated soils can cause health problems including cancer and birth defects.