Extensive Survey of National Wildlife Refuges Reveals Widespread Mercury Contamination Risks to Protected Fish and Wildlife

A new study of 30 National Wildlife Refuges reveals that most sites face moderate to high mercury risk, using dragonfly larvae to track toxic accumulation.

By: AXL Media

Published: Mar 25, 2026, 5:19 AM EDT

Source: Information for this report was sourced from Wiley

Mapping Toxic Accumulation in the National Refuge System

The National Wildlife Refuge System, the world's most expansive network of land and water dedicated to conservation, is facing a varying but persistent threat from mercury pollution. In a comprehensive assessment recently published by investigators, researchers analyzed the chemical footprint across 30 different refuges throughout the United States. The study provides a critical look at how mercury—a potent neurotoxin—is distributing itself within these supposedly protected environments. By establishing these baseline measurements, the U.S. Fish and Wildlife Service aims to create a roadmap for future management actions designed to curb the bioaccumulation of heavy metals in sensitive ecosystems.

Dragonfly Larvae as Sentinels of Ecosystem Health

To gauge the level of contamination, scientists collected 1,356 dragonfly larvae between 2021 and 2023. These insects serve as ideal biological indicators because they spend their larval stage in the water and occupy a mid-level position in the food chain, where they accumulate mercury from their environment and prey. The findings showed a staggering range of concentrations, with some sites recording less than 3 ng/g while others exceeded 2,200 ng/g dry weight. This spectrum mirrors the highest levels ever observed in other protected lands, suggesting that conservation status alone does not shield a waterbody from atmospheric or industrial mercury deposits.

The Prevalence of Moderate and High-Risk Sites

One of the most concerning revelations of the study is the prevalence of significant exposure. Roughly 80% of the refuges sampled contained sites classified as having a moderate or higher risk of mercury contamination. This widespread presence suggests that mercury is not an isolated issue but a systemic challenge for the National Wildlife Refuge System. The identification of these high-risk zones allows refuge managers to pinpoint exactly where fish and wildlife are most vulnerable, enabling more targeted interventions to prevent the toxin from moving further up the food chain to apex predators and humans.