The birds were found on Friday at a rubbish tip and near a quarry site in the Perth suburb of Henderson.
Ken Raine, environmental hazards manager of the DEC Pollution Response Unit, said that birds were seen frothing at the mouth and staggering around at the site before scores of dead birds were discovered within a kilometre radius of the landfill site.
“Autopsies carried out on the birds found Fenthion in high concentration,” the DEC told The Times. “It was in a landfill site and the birds were found close to the site, but we don’t yet know where the pesticide came from.”
Fenthion is an organophosporous insecticide used in horticulture to control pests such as fruit fly and aphids and pest birds such as weaver birds. It is also sold for domestic use to control fleas on dogs and in domestic fruit fly sprays.
The DEC was unable to say what quantity of the pesticide would have been present to kill birds in such large numbers.
Birds began dropping out of the sky in the beachside Perth suburb of Woodman Point over several days last July, sparking a big investigation into local industries. Post-mortem examinations on dozens of carcasses failed to establish a cause of death, but Fenthion poisoning was ruled out at the time, according to the DEC.
In December 2007, 5000 birds including yellow-throated miners, honey eaters and wattle birds were killed by lead carbonate blowing through Esperance as it was being exported through the town’s port.
An investigation into the birds’ deaths found that local children and adults had dangerously high levels of lead in their blood. A local company, Magellan Metals, escaped prosecution over the way it handled the transportation of lead through the town, but fears remained over the potential threat to humans.