cons iderably within the fores eeable future.’ And indeed a s tudy made in Holland in the early
1950s provides s upport for the view that polluted wate rways may carry a cancer hazard. Cities
receiving their drinking water from rive rs had a higher death rate f rom cancer than did thos e
whose water came from sources presumably less s usceptible to pollution s uch as wells. Ars enic,
the envi ronme ntal s ubs tance mos t clearly established as causing cancer in man, is involved in
two his toric cas es in which pollute d wate r s upplies caus ed wides pread occurrence of cancer. In
one cas e the ars enic came from the s lag heaps of mining operations , in the other from rock
with a high natural content of ars enic. Thes e conditions may eas ily be duplicated as a res ult of
heavy applications of arsenical insecticides. The soil in s uch areas becomes pois oned. Rains
then carry part of the arsenic into streams, rivers, and reservoirs, as well as into the vas t
s ubterranean s eas of groundwate r.
Here again we are reminded that in nature nothing exis ts alone. To unders tand more clearly
how the pollution of our world is happening, we mus t now look at another of the earth’s bas ic
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