Investigators have ruled out water, air and soil as the source of contamination on the farm that had supplied dioxin-tainted eggs to a Miaoli County store last week, according to COA officials in charge of livestock matters.

According to Focus Taiwan, the officials said the investigation is now focused on the feed used on Hung Chang Chicken Farm.

According to COA, the farm changed hands two month ago between two cousins, who had both been making feed.

Last Friday, over 42,000 chickens on Hung Chang farm were culled and incinerated by officials from the county's Department of Agriculture and Animal Disease Control Center. Some 15 metric tons of eggs were also scheduled to be destroyed that day.

Meanwhile, of the 8,962 kilograms of eggs that were removed from store shelves as a precautionary measure, 3,730 kg were found to be free of dioxin and have been released for sale, while the rest will be destroyed, the Food and Drug Administration (FDA) said Friday.

Recent tests found 2.88 pg/g and 3.34 pg/g of dioxin, respectively, in two eggs from Hung Chang farm, above the permissible level of 2.5 pg/g. One pg, or picogram, is one trillionth of a gram.

Dioxins, a group of highly toxic and potentially carcinogenic chemicals, are pollutants produced as a result of human activity such as trash burning and can accumulate in the food chain, mainly in the fatty tissue of animals.

Dioxins can damage the immune system, interfere with hormones and cause cancer and reproductive and developmental problems, according to the World Health Organization.

On 21 April, the Food and Drug Administration (FDA) ordered eggs from three farms in Changhua County's Fangyuan Township to be pulled from store shelves as a precautionary measure after excessive levels of dioxins were found in an egg from the area.

After investigation, two of the three farms were cleared and Hung Chang was identified as the source of the problem.

The owners of the other two farms are demanding compensation from the government for loss of revenue.