Everyone loves a good mystery.

Fred Cohen stumbled on one a few months: on an April morning, when there was still snow on the ground, Cohen was walking by the banks of the Humber River at James Gardens in north Etobicoke. He spotted white and blue lentil-size pellets among twigs and grass.

For Cohen, the mystery was not in what they were: nurdles.

“Nurdles were a new thing in the ’60s, and my father worked in the tool-and-die industry and brought them home when they were new,” he said of the plastic pellets. “That is how I recognized them.”

Cohen isn’t a sleuth; he’s a busy contractor. But he figured that the nurdles just didn’t show up at one spot, they had to be flowing down from somewhere. During the next few days, he scoured the Humber at different locations across the city and found nurdles in eight spots.

He went to Crawford Jones Park, near Dee Ave. just south of Hwy. 401, and found a pond where nurdles were floating as the ducks swam.

He went to Summerlea Park, near the Humber, and found nurdles.

He went to the valley below Humber College and found nurdles.

He even went to the Claireville Reservoir, west of Hwy. 427 and south of Hwy. 407, and found nurdles.

They weren’t just in one spot on the shores but all over the place. Cohen says he could easily pick up 20 or 30 pieces in a square foot of debris within minutes.

Cohen took samples and stashed in Ziploc bags — he still has them, the date and the location clearly scrawled on one side.

So where did these nurdles come from? How long have they been resting on the banks of the Humber?

It’s a mystery — one that the Humber could have done without.

Like all plastic, nurdles are harmful to the environment, the fish, the ducks. A nurdle is a tiny plastic pellet — about five millimetres in diameter — and hundreds and thousands of these pellets are melted and put into moulds to form everything plastic. Whatever you see that is plastic likely began as hundreds of thousands of tiny nurdles. They are of different types and they can be clear or coloured.

These micro-plastics are an imminent threat to wildlife, says Nancy Goucher, water program manager with Environmental Defence, an environmental action agency.

“Birds and fish may eat these plastic beads thinking they are food,” she said, adding that nurdles take up space in the stomach and create a fatal blockage. It can quickly lead to their starvation.

“And we have to consider that human beings could eat fish with accumulated plastic in it. What does that mean? . . . It can’t be good.”

Nurdles make Maria Dittrich angry.

An assistant professor at University of Toronto with an expertise in ecology of aquatic systems, Dittrich said nurdles might be very small, “but they can absorb and transport a lot of metal on them. We don’t know how bad that could be as they go through the whole food chain.”

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Lorena Rios-Mendoza, an oceanographer at the University of Wisconsin-Superior, and her team recently sampled sections of Lake Erie and discovered that the water has been invaded by nurdles. They measured concentrations between 1,500 and 1.7 million particles per square mile, which is almost 25 per cent greater than what they had found in the Atlantic Ocean’s debris. (The Atlantic and the Pacific are known to have huge floating plastic debris fields.)

Rios-Mendoza’s team also found that fish were eating nurdles.

Regarding the Humber, Dittrich says it is a scary thought that the microplastics are so close to the city. “As far as I know, it is almost impossible to clean them up. So I don’t know what we are going to do.”

Cohen, meanwhile, standing on the banks of Humber at James Gardens, has a theory.

He says his understanding after speaking to a Toronto city official is that there was a factory fire “somewhere up the river, but he knew nothing more specific.”

(Cohen called 311, the city helpline, told officials everything he had found and asked them to investigate.)

However the nurdles found their way into the Humber, they are now draining into Lake Ontario. A couple of weekends ago, Cohen and a friend found nurdles at the mouth of the Humber near the bicycle bridge.

“That can’t be good, right,” he said.

Ellen Leesti, a city spokesperson, said any possible spill in the Humber would be the responsibility of the provincial Environment Ministry.

Ministry spokeswoman Kate Jordan said she hadn’t heard of any reports of contaminants found in the Humber. She promised to have it looked into.

A couple of days ago, ministry officials contacted Cohen and he agreed to accompany them to the many locations in Toronto where he discovered nurdles.

“I’m happy to do it,” said Cohen, a busy contractor. “Nature can’t speak for itself so someone has to.”