Abstract:

Stamp sand, a residual byproduct of early 20th-century copper mining in Michigan’s Keweenaw Peninsula, poses an escalating threat to aquatic ecosystems and food security for Indigenous communities. In particular, the continued encroachment of stamp sand into Buffalo Reef – a critical spawning ground for Lake Whitefish – has coincided with a concerning decline in fish reproduction. However, the specific impacts of stamp sand on early developmental stages of aquatic species remain poorly understood. To address this gap, we used zebrafish (Danio rerio) as a model organism to evaluate the developmental toxicity of stamp sand exposure. In our previous study, embryos exposed to increasing concentrations of stamp sand (0%, 50%, and 100%) exhibited significant damage to lateral line neuromasts, including reductions in sensory hair cells and claudin B-expressing support cells. While cardiac function remained unchanged, exposed embryos demonstrated decreased hatching success and reduced overall survivability, indicating sublethal but developmentally significant toxicity. Building on these findings, we hypothesized that stamp sand exposure would also induce craniofacial abnormalities, including structural damage and misorganization of cartilage. Contrary to expectations, no overt craniofacial defects were observed. However, statistical analysis revealed increased variability in cartilage shape and size among exposed embryos, suggesting subtle developmental perturbations not detectable through gross morphological assessment alone. These findings highlight the potential for long-term ecological damage and underscore the need for environmental remediation and policy action.