Effects of hollow glass microspheres on cold-water pelagic copepods and fish

The highly reflective properties of hollow glass microspheres (HGM) have motivated their application as a reflective shield onto Arctic sea ice to increase albedo and reduce melting. However, to ensure safe application in the environment, their potential environmental impacts must be assessed. While most HGMs will be positively buoyant in seawater and thus remain in the upper part of the water column, small, cracked and broken HGMs will sink. In this study, we conducted a series of experiments to investigate interactions between HGMs and cold-water pelagic copepods (Calanus finmarchicus) and fish (Gadus morhua) to assess potential acute and chronic toxicity of HGM exposure. Although no visual signs of HGM adhesion onto fish egg chorion or body surfaces of fish larvae and copepods were evident, fish larvae, copepodites and adult copepods ingested HGMs. HGMs in the digestive tract of the two species did not cause acute mortality, and adult copepods were able to rapidly excrete ingested HGMs through fecal pellets. However, prolonged exposure (17 days) of copepodites to HGM concentrations in the range 1-100 mg L^-1 caused reduced lipid accumulation and survival, suggesting that continuous HGM filtration affects copepod energetics. The same exposure concentrations during naupliar development did not cause mortality or developmental effects, but higher HGM concentration (1000 mg L^-1) did. For fish larvae, more information is needed to assess if foraging on HGMs can impact growth and development, as we observed for copepodites.