Bangladesh’s leather tanneries are notoriously filthy, exposing workers and the surrounding neighbourhood to toxic chemicals. And recent studies show that poultry feed produced from industry scraps may also be putting the health of millions throughout the country at risk.

“The whole nation is under threat as chicken is the most consumed meat, and also the cheapest source of animal protein,” said Abul Hossain, a chemistry professor at the University of Dhaka, who led recent studies on how chromium, a tannery waste product, is transported into chicken meat.

According to the Bangladesh government’s department of environment (DoE), tanneries in Hazaribagh, an industrial neighbourhood in Dhaka, emit around 21,600 cu m of toxic waste each day.

The tanneries also generate as much as 100 tonnes per day of scraps - trimmed raw hide, flesh and fat - which are processed into feed by neighbourhood recycling plants and used in chicken and fish farms across the country.

Although the maximum recommended daily dose of chromium has not been established, a review by the European Food Safety Authority stated that a 60kg person could tolerate up to 0.25mg of chromium per day, and noted that carcinogenic chromium “hexavalent” should be kept “as low as possible” in all foods.

“We have found chromium ranging from 350 to 4,520 micrograms (0.35 to 4.52mg) per kg in different organs of chickens which were fed the tannery scraps feed for two months,” said Hossain.

A 2013 study argued that boiling and sun-drying can convert chromium into the carcinogenic “hexavalent” form also known as “Cr (VI).” The study estimated up to 25% of the chickens in Bangladesh contained harmful levels of Cr (VI).