Persatuan Tindakan Alam Sekitar Sungai Petani (PTAS) said lab tests commissioned by the group revealed high levels of barium, cadmium, copper, lead, zinc, iron and aluminium in the sludge and surrounding soil.
The tests, which followed US Environmental Protection Agency standards, found that the level of cadmium which is commonly used in batteries was seven times higher than acceptable limits at 20.7mg/kg.
Zinc levels were 6,312mg/kg, far above the acceptable level of 200mg/kg, while copper levels were at 7,576mg/kg against the acceptable level of 400mg/kg.
Lead levels hovered at 244.9mg/kg, just below the 300mg/kg limit.
The lab report said these metals could seep into nearby water tables and pollute bodies like rivers.
“Heavy metals will accumulate in the organisms that consume the contaminated water or crops and lead to various sicknesses,” it added.
PTAS medical adviser Dr Sunny Tneoh said the group first found the piles of sludge at a site near Taman Songket.
He said the sludge, which smelled foul, appeared to comprise remnants of circuit boards and other computer components which had been burnt by recyclers.
After smelting, he said, gold, silver and other precious metals would be extracted and the leftovers turned into sludge which ethical recyclers would dump using scheduled waste collectors.
However, this method costs tens of thousands of ringgit. Tneoh said many recyclers are now cutting corners by hiring lorry drivers to dump the sludge for a fraction of the price.
“After they noticed us taking samples from the sludge, they cleared it and dug a trench. Then they buried the sludge. This is a disaster waiting to happen,” he added.
PTAS previously said that illegal plastic recycling factories were polluting the air in Sungai Petani. The Kedah government responded by shutting down over 20 factories and sealing their equipment.
However, PTAS maintains that some factories have continued to operate as usual despite being sealed.
The Department of Environment meanwhile dismissed PTAS’ claims of poor air quality, saying levels have been moderate for a long time.