50 years later, DDT still contaminates New Brunswick Lakes

You would never imagine what you would find if you went lake fishing in northern New Brunswick. The water is cold, clear, and seemingly untouched, as you would expect. But lurking beneath the surface, inside the very fish people prize for dinner, lies a chemical ghost from the 1950s: DDT. A study published in [PLOS ONE] shows that this once-celebrated insecticide, banned decades ago, continues to shape the ecology of Canadian lakes. Researchers Joshua Kurek, Meghan Fraser, Bobby Nakamoto, Karen Kidd, and Christopher Edge, conducted a study that revealed that brook trout in lakes once sprayed with DDT carry concentrations of the breakdown products of the pesticide at levels **ten times higher than what’s considered safe for wildlife consumers**. DDT, short for dichlorodiphenyltrichloroethane, was hailed as a miracle chemical when it emerged in the 1940s. It killed mosquitoes, ticks, lice, and crop pests with stunning efficiency. During World War II, it was sprayed over soldiers to prevent malaria and typhus. After the war, DDT became a household name, used widely in agriculture, forestry, and even sprayed on suburban lawns. But the wonder chemical had a dark side. By the 1960s, scientists were uncovering alarming patterns: birds of prey like eagles and falcons were vanishing, their eggshells thinned by DDT exposure. Rachel Carson’s landmark 1962 book *Silent Spring* galvanized public concern, eventually leading to bans in North America and Europe by the 1970s. Yet, unlike pests, DDT doesn’t die easily. It lingers in soils and sediments, breaking down only slowly into metabolites called DDE and DDD, which are themselves toxic. These compounds cling to organic matter, settle into lake bottoms, and creep up the food chain. Between 1952 and 1968, **New Brunswick started one of the largest aerial pesticide spray programs in the world**. The goal was to stop outbreaks of the spruce budworm, a moth caterpillar that devours conifer needles and can devastate forests. Planes rumbled over the province’s vast spruce and fir forests, releasing **5.7 million kilograms of DDT over 11.8 million hectares**. By 1993, nearly every corner of New Brunswick’s 6.2 million hectares of forest had been sprayed with some kind of insecticide. The ecological bill for that campaign is still coming due. To understand the legacy of DDT products, the research team studied **seven lakes** in New Brunswick: five “impact” lakes where DDT had been sprayed, and two “reference” lakes outside the spray zone. They collected sediment cores from the lake bottoms, which act like time capsules, preserving layers of pollution. They also caught brook trout, the iconic speckled fish beloved by anglers, and analyzed their muscle tissue for traces of DDT and its metabolites. Stable isotope tests were also run to confirm that the fish were feeding at similar positions in the food web, ruling out diet as the main driver of contamination differences. Unfortunately, the results show that **lake sediments still contain high levels of DDT’s breakdown products**, even 50 years later. In some lakes, concentrations exceed Canadian safety thresholds many times over. Also, **brook trout in sprayed lakes had DDT levels ten times higher** than the Canadian guideline for protecting wildlife. At California Lake, for example, trout carried an average of 179 nanograms per gram (wet weight equivalent), compared with the safe guideline of just 14. In contrast, trout from the two reference lakes had negligible levels, often below detection limits. Most of the contamination came from DDE and DDD, the “weathered” remnants of the original DDT. This shows the problem isn’t new spraying but the **slow leaking of legacy chemicals from sediments into the food chain**. As you might know, brook trout (*Salvelinus fontinalis*) are a cultural icon in Atlantic Canada, a top predator in lake ecosystems, and a crucial link in the food web. When brook trout are contaminated, it signals that everything below them, zooplankton, insects, smaller fish, is touched by the same legacy. The researchers also point out that what affects brook trout ripples outward. Birds, mammals, and even people who consume these fish could be exposed. DDT and its metabolites are known to disrupt hormones, damage nervous systems, and transfer from mother fish to eggs, threatening future generations. The five lakes in the study are just a sample. **The authors estimate that of New Brunswick’s roughly 2,500 lakes, about 500 lie within watersheds that were sprayed with DDT**. That means nearly a quarter of the province’s lakes could host fish carrying unsafe levels of contamination. Even though Canada banned DDT in the early 1970s, the study highlights an unsettling reality: chemicals don’t obey political calendars. What was sprayed from crop dusters half a century ago is still shaping ecosystems today. This story isn’t unique to Canada. Around the world, lakes and rivers bear the chemical fingerprints of the mid-20th century. In Michigan, fish still show traces of DDT. In northern Italy, Alpine glaciers release DDT into downstream lakes as they melt. In parts of Africa and Asia, DDT is still used in malaria control programs, raising concerns about its persistence in soils and waterways. The Canadian findings join a global chorus of warnings: **once unleashed, persistent pollutants like DDT remain part of the ecological fabric for generations**. Careful testing, regulation, and monitoring aren’t bureaucratic red tape; they’re safeguards against repeating mistakes of the past. In their paper, the authors note that local residents still share memories of the era “when the forests were sprayed.” For many, it was an accepted part of life: planes flying overhead, misting forests and lakes. Few could have guessed that the mist would linger invisibly for half a century. Now we know that what seemed like progress in the 1950s is a persistent problem in 2025, but perhaps we can learn the lesson and start avoiding casting such long, toxic shadows in the future. If you want to learn more, read the original article titled "Legacy DDT and its metabolites in Brook Trout from lakes within forested watersheds treated with aerial applications of insecticides" on [PLOS One] at . [PLOS One]: http://dx.doi.org/10.1371/journal.pone.0320665

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