Eggs Reveal Hidden Poison in New Hampshire Lakes

Scientists study abandoned loon eggs to learn about pollution. The eggs that never hatch are collected carefully after the mother has left them. Each egg carries a record of what the loon ate in the weeks before it was laid. Eggs are better than blood samples for this work. Blood shows only the last meal, but an egg reflects a whole month of food and water that the bird has swallowed. Thus eggs give researchers a snapshot of local contamination. Lead fishing weights are one known threat to loons. Birds eat fish that have swallowed lead sinkers or mistake the weights for stones, and this can kill them quickly. Lead remains the top cause of loon deaths in New Hampshire. Another danger is chemical pollution, especially “forever chemicals” called PFAS. These substances travel from water to plankton, then to small fish and crayfish, and finally to loons. Each step concentrates the toxins—a process called biomagnification. Over many years, loons accumulate large amounts of these chemicals. In 2023, researchers tested 144 eggs from lakes across the state.

They found high levels of PFOS, a common PFAS, and other pollutants like PCBs, DDT, dioxins, and fire‑fighting chemicals. Lake Winnipesaukee had the highest PFAS levels. About one‑quarter of all eggs tested had PFOS above safe limits for birds, and most eggs from that lake were over the threshold. The impact of these chemicals on loon health is still unclear. Scientists are not sure if the toxins cause eggs to fail or reduce breeding success. Future studies will look at how PFAS levels in eggs relate to the number of chicks that survive. The pollution may come from many places. One suspect is a former packaging plant on the lake’s east side, now listed as a Superfund site. More testing is needed to pinpoint the source. The state is starting a program to test fish for PFAS in lakes with high egg contamination. This will help determine how far the chemicals travel and who might be affected. Despite these threats, loon numbers are slowly rising. The last count found 862 loons in New Hampshire lakes, up from 844 a year earlier. But pollution, human activity, habitat loss, and climate change still challenge the birds.

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