Several man-made toxic products from agriculture and industry, e.g. mercury, lead, chromium and other toxic compounds, rob years of healthy life from millions each year. These toxic compounds are either emitted to the atmosphere or injected into water. However, arsenic from natural origins in toxic levels can be found in groundwater as well.

Here are only some examples of worst toxic pollutants. Arsenic leaching into groundwater afflicts some 750,000 people, largely in south Asia. This can can lead to abnormal heartbeat, blood vessel damage and cancer, among other ill effects. Dry waste from LEAD–ACID BATTERIES, can cause very fine lead oxide to be inhaled or otherwise absorbed into the body with negative effects on the nerve-system. CARCINOGENIC CHROMIUM used for turning hides into leather is, also, toxic. Clusters of such tanneries in countries such as Bangladesh produce vast quantities of toxic pollution in wastewater or as solid waste. Pesticide Problems in agriculture induce skin irritation and can cause cancer. Industrial wastewater flowing in an open drain with several toxic compounds, for example the Malir River in Karachi, Pakistan, boasts lead levels of 100 times higher than the health standards for irrigation water. Elemental mercury “quicksilver” used in separation of gold in slurry cause development of disorder and affects the central nervous system.  SMELTER, e.g million metric tons of lead are produced annually by separating it from mined ore.

http://www.scientificamerican.com/slideshow/10-worst-toxic-pollution-problems-slide-show/