Smartphone maker Apple Inc gets tangled in yet another controversy, this time involving its suppliers Foxconn Technology Group and Unimicron Technology, alleged to have been dumping toxic wastewater from heavy metals into China's local rivers.

Rotten Apple: Suppliers of Smartphone Maker Alleged to Have Polluted China River

Environmental watchdogs led by Ma Jun, a director of China's Institute of Public & Environmental Affairs, along with four other groups, claimed the two Taiwan-based companies were dumping toxic wastewater from heavy metals into the Huangcangjing and Hanputang rivers. Waters from these two rivers flow into another two sets of rivers, the Yangtze and Huangpu rivers, which in turn supply Shanghai's drinking water for its 24 million residents.

Foxconn has immediately released a statement denying the allegations. It stated that all its emissions from the plant meet relevant laws and regulations. UniMicron, however, has yet to issue a statement.

Moreover, it maintained that whatever emissions going into the rivers could not have been from its plant alone.

"The river that runs through the middle of that industrial park receives waste water discharges from a number of companies that are based in the park," the company said in a statement.

"If you're severely exceeding emissions standards, then we will punish you," Chinese environmental regulator Ding Yudong told The Wall Street Journal, confirming reports the two suppliers were currently being investigated.

Several large plants in a northern industrial part of Kunshan were operated by Taiwanese electronics companies. They produce printed circuit boards, silicon products and laptops, among others. And they actually are allowed to dump wastewater into the river.

However, "the volume and its contents would be under scrutiny," Mr Ding said.

Copper toxicity, according to Ma Jun, poisons the fish in the rivers and soil in the water bed. It can lead to cardiovascular illness in humans.

Quoting figures released by state-affiliated researchers, The Wall Street Journal reported that heavy metals like cadmium may have already contaminated between 8 per cent and 20 per cent of China's arable land, or some 25 to 60 million acres.