Wageningen University is launching a new investigation into mass lobster deaths in the Oosterschelde estuary in Zeeland.

“There are no outward signs of ill health but many of the lobsters are slow and weak. Something is going on but we don’t know what it is,” Wageningen researcher Jildou Schotanus told broadcaster NOS.

An earlier investigation by the university into possible viruses or bacteria did not yield any results. “We are now widening the investigation to include the presence of toxic substances and heavy metals,” she said.

This year’s lobster season has got off to a bad start again, fisherman Henk Jumelet told the broadcaster. Where he would normally catch 25 kilos of lobster, he now catches two and they are in a bad way. “Usually you would have to watch your fingers but they are not moving. It’s not normal,” he said.

Other fishermen have given up completely and have removed their nets from several sites in the estuary.

According to the fishermen, the lobsters are being poisoned by the heavy metals in steel slag, a by-product of steel production widely used in construction, including  the coastal reinforcement of the Ooster and Westerschelde.

The main producer of steel slag is Tata Steel, which sells the stone-like boulders to dealers and contractors.

Last year, public health institute RIVM found that steel slag is a threat to the environment as it contains “all manner of heavy metals” that contaminate groundwater and kills anything that lives in it.

Locals living in areas where steel slag is used have also reported health problems, such as nasal hemorrhaging and burns.

A request from the Zeeland provincial authorities to stop using steel slag until the results of the investigation are clear has been rejected by junior infrastructure minister Vivianne Heijnen.

Heijnen said she is not worried about the environmental effects of steel slag. “If I were I would stop its use immediately,” she said. The steel slag could now still be used to reinforce a channel in the Westerschelde later this year.

However, following a lobby by MPs, local authorities, provincial authorities and monitoring bodies will in future be informed if steel slag is used in construction so they can decide whether or not a location is too vulnerable.