Search

Gigaton scale atmospheric carbon dioxide (CO 2) removal (CDR) is needed to keep global warming below 1.5 °C. Coastal enhanced olivine weathering is a CDR technique that could be implemented in coastal management programmes, but its CO 2 sequestration potential and environmental safety remain uncertain. Large scale olivine spreading would change the surficial sediment characteristics, which could potentially reduce habitat suitability and ultimately result in community composition changes. To test this hypothesis, we investigated the avoidance response of the marine gastropod Littorina littorea (Linnaeus, 1758) and marine amphipod Gammarus locusta (Linnaeus, 1758) to relatively coarse (83 – 332 µm) olivine and olivine-sediment mixtures during short-term choice experiments. Pure olivine was significantly avoided by both species, while no significant avoidance was observed for sediment with 3% or 30% w/w olivine. For L. littorea , aversion of the light green colour of pure olivine (i.e. positive scototaxis) was the main reason for avoidance. Moreover, olivine was not significantly avoided when it was 7.5 cm (45%) closer to a food source/darker microhabitat (Ulva sp.) compared to natural sediment. It is inferred that the amphipod G. locusta avoided pure olivine to reduce Ni and Cr exposure. Yet, a significant increase in whole body Ni concentrations was observed after 79 h of exposure in the 30% and 100% w/w olivine treatments compared to the sediment control, likely as a result of waterborne Ni uptake. Overall, our results are significant for ecological risk assessment of coastal enhanced olivine weathering as they show that L. littorea and G. locusta will not avoid sediments with up to 30% w/w relatively coarse olivine added and that the degree of olivine avoidance is dependent on local environmental factors (e.g. food or shelter availability). [Display omitted] • Pure olivine was significantly avoided by Gammarus locusta and Littorina littorea • Littorina littorea avoided pure olivine due to its light colour (positive scototaxis) • Gammarus locusta likely avoided pure olivine due to its high Ni and Cr content • Olivine was not significantly avoided at concentrations of 3% and 30% w/w [ABSTRACT FROM AUTHOR]

• Olivine exposure results in significant Ni and Cr accumulation in Gammarus locusta. • Metal bioaccumulation was dependent on olivine grain size and concentration. • Chronic reproductive toxicity occurred at 10% w/w olivine. • Ecosystem impacts could limit the scale of coastal enhanced olivine weathering. Active atmospheric carbon dioxide removal (CDR) is needed at a gigaton scale in the next decades to keep global warming below 1.5 °C. Coastal enhanced silicate weathering (CESW) aims to increase natural ocean carbon sequestration via chemical weathering of finely ground olivine (Mg x Fe (1− x) SiO 4) rich rock dispersed in dynamic coastal environments. However, the environmental safety of the technique remains in question due to the high Ni and Cr content of olivine. Therefore, we investigated the short term bioaccumulation and chronic toxicity of olivine in the marine amphipod Gammarus locusta. Acute 24-h olivine exposure resulted in significant grain size dependent olivine ingestion and subsequent Ni and Cr accumulation in tissues. Thousands of small (mainly ≤ 10 µm) olivine grains were ingested by G. locusta , but their importance for trace metal bioaccumulation requires additional research. Most olivine grains were egested within 24 h. Chronic 35-day olivine (3–99 µm) exposure reduced amphipod survival, growth, and reproduction, likely as a result of metal induced oxidative stress and disturbance of major cation homeostasis. Amphipod reproduction was significantly reduced at olivine concentrations of 10% w/w and higher. In the context of ecological risk assessment, application of an arbitrary assessment factor of 100 to the highest no observed effect concentration of 1% w/w olivine yields a very low predicted no-effect concentration (PNEC) of 0.01% w/w olivine. This low PNEC value highlights the urgent need for additional marine olivine toxicity data to accurately assess the environmentally safe scale of coastal enhanced weathering for climate change mitigation. [Display omitted] [ABSTRACT FROM AUTHOR]