As gold makes its way around the world, so too does mercury — poisoning the air and food of people thousands of miles away. Small-scale gold mining is the largest single source of mercury pollution.

A recent study of women on 24 remote islands found that more than half displayed high mercury levels. The women lived far from sources of mercury pollution but ate a diet rich in fish. In the United States, contaminated fish is the No. 1 source of mercury poisoning.

Indonesia, the world’s fourth most populous nation, stands out for its huge number of outlaw gold miners and for concerns that some law enforcement officials assigned to police the trade are instead profiting from it.

As much as anyone, Cece Rifa’i, a former miner, is responsible for Indonesia’s mercury boom and spreading the scourge of contamination across the country.

But he has no regrets.

“I don’t feel guilty about anything,” he said from the veranda of his two-story home on the island of Java.

For years, Mr. Cece was a pioneer in a network of illegal mercury producers, traders and smugglers who supply gold miners across Indonesia with mercury, used to extract gold from crushed ore.