ANTHONY RICCIARDI, a scientist at McGill University, was looking for evidence that an invasive Asian clam had colonised a warm spot in the St Lawrence river when a member of his team made a more headline-worthy discovery. Peering through a microscope at sand scooped up from the riverbed, the student saw hundreds of tiny plastic spheres that stood out for their unnatural roundness and vivid colours.

Microbeads, widely used as an abrasive in toothpaste and face soap, are common in the world’s oceans, lakes and rivers. Scientists had assumed that they floated in fresh water and were flushed downriver to the sea. Now Mr Ricciardi has shown that some sink to the bottom of lakes and rivers, where they are eaten by bottom-feeding fish, some of which, such as yellow perch, end up on dinner plates.

This finding adds to alarm over plastic pollution in the Great Lakes, which contain a fifth of the world’s fresh surface water. Sherri Mason, a chemist at the State University of New York in Fredonia, found 1m plastic particles per square kilometre in Lake Ontario. According to a team from the University of Waterloo, the Great Lakes have as much debris as ocean gyres (rotating currents), where the problem is better known. Industry and governments are beginning to tackle it.

“Ugelstad spheres”, named after the Norwegian who invented them in 1976, have uses in cancer research, the treatment of HIV and the manufacture of flat-panel televisions. Only in the past decade has the cosmetics industry discovered how useful they are for scrubbing teeth and faces.

Too tiny to be caught by municipal water filters, they flow into lakes and rivers. New Yorkers rinse 19 tonnes of microbeads down drains each year. In water they can break down, releasing toxins that are used in their manufacture, or become coated with other poisons, such as PCBs. Fish that eat them develop diseases. Less is known about what happens to people who eat the fish. Dentists report finding the tiny orbs in patients’ gums.

Makers of toothpaste and facial scrubs have started to take action. Unilever and Colgate-Palmolive have stopped using microbeads; Procter & Gamble and Johnson & Johnson say they will follow in 2017. Loblaws, Canada’s largest retailer, will remove them from its in-house brand. But these companies want governments to ban the use of microbeads by all manufacturers, so that none has an unfair advantage.

On July 30th Canada’s labour minister announced by the shores of Lake Ontario that the government would declare microbeads to be a toxic substance and prohibit the manufacture, import and sale of “personal-care” products that contain them. Eight American states have passed bans, starting with Illinois in 2014. The Illinois ban does not apply to biodegradable microbeads, whose safety is unproven (it is unclear whether or not Canada’s will). California and New York are considering tougher restrictions. Four European countries, led by the Netherlands, are pressing the EU to prohibit their use in cosmetics.

Scientists have moved on to investigate other worrying materials. Mr Ricciardi’s team has found microfibres from synthetic textiles in the digestive tracts of fish. If brushing your teeth is bad for wildlife, doing your laundry could be worse.