Tap water in Tokyo is not infected with Cryptosporidium, a microscopic parasite that caused diarrhea and stomachaches in more than 8,700 Saitama residents in 1996, the Tokyo Metropolitan Government said on Thursday.

The results were based on surveys conducted at water purification plants in Tokyo, which detected no cases of the protozoan in processed water. The parasite is believed to cause diarrhea because it is resistant to chlorine, which is the main purifying agent added to tap water.

Cryptosporidium is found in human and livestock excrement, together with colon bacilli, metropolitan government officials said. The government conducted surveys at plants where colon bacilli were found in untreated water.

In a separate survey also released Thursday, the metropolitan government said that levels of dioxin in Tokyo tap water are either zero or negligible. Dioxin is an extremely toxic chemical byproduct that is produced when plastic resins are burned.

Of 10 tests on processed water at seven major water purification systems, nine detected no dioxin and one showed 0.012 picogram of dioxin toxicity per liter. That amount is equal to less than 1/20,000 of the tolerable daily intake for an adult male weighing 50 kg, a level set by the Health and Welfare Ministry, the officials said.

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