Assertion: arsenic's effect | /r/HasProperty | seen below about 150 parts per billion
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text: Skin pigmentation, keratoses and skin cancers were found by Tseng in Taiwan in 1966 among people who drank from arsenic contaminated wells (but no effect was seen below about 150 parts per billion (ppb), which might therefore be a biological threshold) and a very high incidence of lung, bladder and other cancers was found in Taiwan by Dr Chien-Jen Chen in 1986 and by Dr Allan Smith and collaborators in Chile in 1993.