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Of all the winter pollutants, road salt, which lowers the freezing point of water, is the most concerning because it is particularly harmful to freshwater organisms that haven’t evolved to tolerate salt water, experts say.
“The reason this is an environmental issue for aquatic ecosystems is that salt specifically, is toxic,” said Andrew Hrycyna, water quality program manager at the Mystic River Watershed Association.
Hrycyna said the Environmental Protection Agency sets threshold levels for exposure to chloride, a part of salt that dissolves in water. Over time, such exposure can stunt growth and reproduction in fish and aquatic insects, while sudden exposure can cause them to die instantly.
Data collected for over 20 years by the Mystic River Watershed Association show an upward trend in chloride levels in freshwater sites across the waterbodies. The group measures “specific conductance,” a measurement of the electrical conductivity of water which is directly proportional with salt content, and has documented rising levels not only in winter but year round, suggesting that groundwater itself is becoming saltier.
A 2016 study by the United States Geological Survey found similar increases in chloride concentrations across rural and urban parts of New England, reinforcing concerns that the use of road salt has long-term regional impacts.
In Alewife Brook, a tributary of the Mystic River, chloride concentrations spiked sharply during snowmelt and rain events, monitoring during winter storms has shown. In some cases, levels briefly exceeded acute toxicity thresholds for freshwater organisms. Alewife Brook is now officially listed as “impaired” by chloride on Massachusetts’ Integrated List of Waters.
“The big problem comes not from the fact the snow melts, it’s the sheer volume [of salt] we’re using,” Hrycyna said. “We know we have to put some salt down to keep people safe, but can you put less and keep people equally safe?”
In most neighborhoods, storm drains are directly connected to nearby bodies of water through an underground pipe network. Anything on the street — from sand and soot, to dog waste and plastic debris — can be swept into rivers during snowmelt.

“It’s still precipitation,” said Chris Mancini, executive director of Save The Harbor/Save The Bay. “It’s still landing on urban streets, and where it melts, it’s carrying whatever it’s captured into storm drains over land into the water.”
Some cities, like Cambridge, are experimenting with brine, salt dissolved in water and sprayed onto roads, which allows for precise application and reduced overall use.
But there are other pollutants.
That black, crusty layer visible on plowed snow contains accumulated car exhaust particles, microplastics, sand and bacteria from pet waste. In the Charles River, elevated bacteria levels have the potential to make people sick. Nutrient pollution — including phosphorus from fertilizers, detergents and even organic matter like fallen leaves — can lead to over-fertilizing the river.
“It’s essentially like dumping fertilizer into the river, and you just get way too much plant growth, and it can actually overwhelm the river’s ecosystem,” said Julie Wood, climate resilience director at Charles River Watershed Association.
Advocates say the solution lies in redesigning how cities handle runoff.
Mancini said Boston’s Deer Island treatment plant and stormwater tunnels help manage intense runoff, storing and gradually releasing water to avoid overwhelming the system.
Green stormwater infrastructure, first pioneered in Maryland in the 1990s, is another part of the solution. These systems, which can take the form of sunken gardens, tree pits or underground infiltration tanks, capture runoff before it reaches storm drains. Soil and plant roots filter pollutants while water slowly seeps into the ground.
“That’s what we’re always pushing for both rainfall runoff and the snow melt,” Wood said. “Just natural filtration before it reaches the river.
Wood said salt remains harder to filter because it dissolves easily and can damage plants used in green infrastructure systems. That makes reducing salt use at the source especially critical. Mancini suggested the use of environmental friendly salt as an alternative.
There is, however, one environmental benefit to heavy snowfall. Wood said slow, gradual snowmelt allows water to recharge groundwater supplies, something intense rainstorms often fail to accomplish.
Still, advocates say the sight of blackened snowbanks offer a powerful visual reminder.
“Snow is just revealing to our eyes the pollution that’s always there year-round,” Wood said. “That black stuff we see on the snow is not only there in the winter, it’s just only visible in the winter.
Aayushi Datta can be reached at aayushi.datta@globe.com.
Boston Marathon
In our “Why I’m Running” series, Boston Marathon athletes share what’s inspiring them to make the 26.2-mile trek from Hopkinton to Boston. Looking for more race day content? Sign up for Boston.com’s pop-up Boston Marathon newsletter.
Name: Brianna Poehler
City/State: Granby, Mass.
I am running the 2026 Boston Marathon with Miles for Miracles in support of Boston Children’s Hospital. The Boston Marathon is deeply personal to me and my family.
My daughter is a liver transplant survivor, and at just 11 months old, she received a life-saving liver transplant at Boston Children’s Hospital.
What could have been the most devastating chapter of our lives became a story of hope, resilience, and extraordinary care because of the BCH team.
When our daughter was so small and so sick, the doctors, nurses, and staff at Boston Children’s carried us through the unimaginable.
They combined world-class medical expertise with compassion that went far beyond treatment plans and hospital rooms. They cared for our daughter as if she were their own. They supported us as anxious, exhausted parents. They gave us answers when we had questions, and reassurance when we were overwhelmed.
Most importantly, they gave our daughter a second chance at life.
Today, she is thriving because of that gift. Every milestone she reaches is a reminder of the miracle she received and the team that made it possible. Running the Boston Marathon is my way of honoring that gift and saying thank you in the most meaningful way I can.
The marathon is a test of endurance, determination, and heart — qualities I saw in my daughter during her fight and in the Boston Children’s team every single day.
With every mile I run, I will be thinking of her strength, her transplant journey, and the families who are walking similar paths right now.
By running with Miles for Miracles, I hope to raise funds that will support groundbreaking research, life-saving treatments, and compassionate care for children like my daughter. This race is more than 26.2 miles — it is a celebration of survival, gratitude, and hope.
Editor’s note: This entry may have been lightly edited for clarity or grammar.
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Charlotte Hornets (31-31, ninth in the Eastern Conference) vs. Boston Celtics (41-20, second in the Eastern Conference)
Boston; Wednesday, 7:30 p.m. EST
BETMGM SPORTSBOOK LINE: Celtics -6.5; over/under is 214.5
BOTTOM LINE: Charlotte is looking to keep its five-game win streak alive when the Hornets take on Boston.
The Celtics are 27-13 against Eastern Conference opponents. Boston is sixth in the NBA with 46.2 rebounds led by Nikola Vucevic averaging 8.8.
The Hornets are 19-21 in conference matchups. Charlotte is 7-8 when it turns the ball over less than its opponents and averages 15.0 turnovers per game.
The Celtics average 15.5 made 3-pointers per game this season, 2.7 more made shots on average than the 12.8 per game the Hornets allow. The Hornets average 16.0 made 3-pointers per game this season, 2.1 more made shots on average than the 13.9 per game the Celtics allow.
TOP PERFORMERS: Jaylen Brown is averaging 29 points, 7.1 rebounds and five assists for the Celtics. Payton Pritchard is averaging 17 points and 5.8 assists over the past 10 games.
Kon Knueppel is averaging 19.2 points, 5.5 rebounds and 3.5 assists for the Hornets. Brandon Miller is averaging 22.7 points, 5.3 rebounds and 3.6 assists over the past 10 games.
LAST 10 GAMES: Celtics: 8-2, averaging 109.4 points, 50.7 rebounds, 27.1 assists, 6.1 steals and 6.4 blocks per game while shooting 45.7% from the field. Their opponents have averaged 98.5 points per game.
Hornets: 7-3, averaging 117.3 points, 47.8 rebounds, 27.4 assists, 8.5 steals and 4.2 blocks per game while shooting 45.6% from the field. Their opponents have averaged 106.2 points.
INJURIES: Celtics: Jayson Tatum: out (achilles), Neemias Queta: day to day (rest).
Hornets: Coby White: day to day (injury management).
___
The Associated Press created this story using technology provided by Data Skrive and data from Sportradar.
Today is a First Alert weather day. A system to our south is pushing mix of snow and rain into southern New England through this evening and tonight.
For us here in Greater Boston, expect snow to continue spreading over our area through the afternoon/evening commute. In fact, parts our area could see up to 1 to 2 inches of snow accumulation before the sleet and rain move in.
Much of Greater Boston will likely see snow amounts on the lower end. Higher snow amounts are expected toward southern New Hampshire and along and north of outer Route 2. Also, some ice accumulations are possible, up to a tenth of an inch, creating a thin glaze here and there.
Dozens of schools in Connecticut and Massachusetts have already announced early dismissals as a result of the storm.
While this system won’t cripple our area, conditions could still create a mess on the roads during the evening commute through tonight. Be careful while driving. A Winter Weather Advisory remains in effect for parts of our area through early Wednesday morning. High temperatures will be in the mid to upper 30s today. Overnight lows will drop into the low 30s.
We’ll wake up to patchy fog Wednesday morning before the sun returns. High temperatures will be in the upper 40s. We’ll stay in the 40s on Thursday with increasing clouds. But by late Thursday night into Friday, wet weather returns. Some snow could mix with the rain into Friday morning. Highs will be in the upper 30s Friday.

Warmer weather is expected this weekend. Highs will be in the 50s Saturday and possibly near 60 on Sunday.
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