PORTLAND — With Tuesday’s storm, Portland topped 90 inches of snow for the season, about 50 percent more than the city’s average winter accumulation.

Portland’s high numbers are largely representative of average-topping snowfall figures around southern and central Maine, and that’s bad news for state bays and waterways, environmentalists said Tuesday.

“It looks pretty on the surface, but what happens when it melts?” asked Carrie Kinne, executive director of the Bath-based Kennebec Estuary Land Trust.

Joe Payne, Casco Baykeeper for the environmental advocacy group Friends of Casco Bay, said the phrase “pure as the driven snow” is a misnomer. Snowflakes, more so than rain, absorb pollutants from the air on their way to earth, and then add chemicals and trash from the roadways when they land.

While many people recognize that heavy rains wash street chemicals and pollutants into water bodies, Payne said snow is perhaps more dangerous to the environment.

“Snow is really a good scavenger of air pollution,” Payne said.

Toxic metals, like lead, at their molecular level can be captured by the crystallized flakes in their descent. But what makes heavy snow seasons like this one perhaps more concerning to environmentalists is what happens when those flakes build up on the ground.

“What’s different today about snowfall, compared to rain, is that we’re saving it,” Payne said. “It’s that accumulation of pollutants that makes it unique.”

Portland typically sees about 60 inches of snow each winter. This winter, the city was slammed by a record 31.9 inches in one Feb. 8-9 snowstorm on its way toward what is, so far, a 90-plus-inch snow season.

So while the rain washes chemicals into waterways, he said, snow is pushed into large piles on storage lots, where it gathers a season’s worth of those chemicals in isolated spots. The pollutants gathered are in cases more intense as well, as many municipalities utilize road salts featuring cyanide during the winter months.

Payne said the road salt cyanide — which is in a safer elemental form when initially used on the roads, but breaks down into its more recognizable deadly form when exposed to higher acidity or sunlight — can be seen in snow piles as blue streaks.

Payne said federal regulations cap cyanide discharges into freshwater bodies at 20 parts per million, and because of the greater sensitivity of aquatic life in the oceans, at 1 part per million in salt water bodies. Yet he said that while the state forces snow dumps to be located 100 feet or farther from freshwater, snow piles can be kept as close as 20 feet to salt water.

He said the Friends of Casco Bay two years ago successfully fought to remove a provision from state snow dumping laws that allowed permits for disposing of snow directly in freshwater bodies, and said the South Portland-based organization plans to lobby for the striking of a similar provision that still allows occasional dumping in salt water — which he said approximately six Maine municipalities are permitted to do.

When the spring thaw comes, the snow piles all over the state melt and carry all of winter’s road chemicals, trash and air pollution into the rivers, creeks, streams and the ocean. That concentrated blast, Payne said, can cause deadly toxic shock to marine life — and with much higher than average snowfall this season, that concentrated blast could be much more lethal.

Kinne said she can watch the spring runoff from her organization’s office overlooking Front Street in the riverfront city of Bath.

“This street goes downhill gradually. When I’m seeing the snow melting, you see the water in oil-slicked streams going downhill. You can see streams of water that just have this sheen to them, heading right down to the river,” Kinne said.

“Is that (one-time snowmelt) worse than putting the same amount of chemicals in over a period of eight months? I’m not going to argue that. [Pollutants] shouldn’t be going in at any time,” Payne said. “But when it comes all at once in a rush, it can kill things. It creates toxic shock.”

Kinne said her organization is planning an April 20 storm drain stenciling event, in which community members are being invited to stencil small reminders near Bath storm drains about where those drains lead.

“Whatever we put down storm drains winds up in our waterways, where we enjoy fishing, boating or swimming,” she said. “Before, [pollution could be mostly traced to] big companies. Now it’s more human use — it’s cars, it’s dogs, it’s us putting our pharmaceuticals into the water. It’s easier (to advocate against) when it’s a big corporation. How do you let people know that things they are doing are having an effect? Or that changes they make can have an effect?”