Acute bioaccumulation and chronic toxicity of olivine in the marine amphipod Gammarus locusta

Olivine-induced seasonal dynamics of eukaryotic microalgal and bacterial assemblages in mid-latitude nearshore marine ecosystems

Ocean alkalinization, especially through olivine addition, represents a promising strategy for reducing atmospheric CO2 levels. The addition of olivine may have seasonal impacts on marine microalgal and bacterial communities, which have not been studied yet. In this study, controlled laboratory experiments were conducted in spring and autumn to measure the responses of microalgal and bacterial communities to olivine addition in different seasons. Our findings revealed that both communities demonstrated different seasonal response patterns. Olivine addition had no significant effect on Diatomea community succession in the spring experiment, while in autumn, it enhanced the competitive advantage of Thalassiosira under the availability of nitrogen and phosphate. The bacterial community structure exhibited minimal changes after olivine addition in spring, while significant shifts were observed, predominantly influenced by the succession of microalgae in autumn. Candidatus Actinomarina showed a strong correlation with the Thalassiosira, suggesting a possible link between the two microorganisms in terms of element utilization. Furthermore, bacteria (Methylobacterium-Methylorubrum in spring and Marivivens in autumn) with a tendency for particle adhesion increased following the addition of olivine in both seasons, however, the concomitant alterations around the olivine microenvironment might be deleterious to their growth. The present investigation underscores the significance of the application timing, which has important implications for olivine-based ocean alkalinization.

Potential Environmental Impacts and Management Strategies for Metal Release during Ocean Alkalinity Enhancement Using Olivine

Ocean alkalinity enhancement (OAE) based on enhanced weathering of olivine (EWO) is a promising marine carbon dioxide removal (mCDR) technique. Previous research primarily focuses on the toxicological effects of potentially toxic metals (PTMs) released from olivine. In this Perspective, we explore the overlooked impacts of EWO on environmental media in two scenarios: olivine applied to beaches/shallow continental shelves and offshore dispersion by vessels. We analyze the potential migration pathways of iron and PTMs (e.g., nickel and chromium) after their release, and their interactions with manganese oxides in sediments, potentially causing secondary contamination. Additionally, we propose mitigation strategies to prevent PTM concentrations from exceeding local environmental quality standards, including the use of alkalization equipment to control PTM levels. This Perspective underscores the need for thorough environmental assessments prior to large-scale implementation to ensure the sustainability and efficacy of mCDR efforts.

Sustainable carbon sequestration via olivine based ocean alkalinity enhancement in the east and South China Sea: Adhering to environmental norms for nickel and chromium

Enhancing silicate weathering to increase oceanic alkalinity, thereby facilitating the absorption of atmospheric carbon dioxide (CO2), is considered a highly promising technique for carbon sequestration. This study aims to evaluate the feasibility and potential of olivine-based ocean alkalinity enhancement (OAE) for the removal of atmospheric CO2 and its storage in seawater as bicarbonates in the East and South China Seas (ESCS). A particular focus is placed on the potential ecological impacts arising from the release of nickel (Ni) and chromium (Cr) during the olivine weathering process. We considered two extreme scenarios: one where Ni and Cr are entirely retained in seawater, and another where they are completely deposited in sediments. These scenarios respectively represent the maximum permissible concentrations of Ni and Cr in seawater and sediments during the OAE process. Current marine environmental quality standards (EQS) were utilized as the threshold limits for Ni and Cr in both seawater and sediment, with concentrations exceeding these EQS potentially leading to significant adverse effects on marine life. When all released Ni is retained in seawater, the allowable dosage of olivine varies from 0.05 to 13.7 kg/m2 (depending on olivine particle size, temperature, and water depth); when all released Ni is captured by sediment, the permissible addition of olivine ranges from 0.21 to 2.1 kg/m2 (depending on mixing depth). Given the low solubility of Cr, it is not necessary to consider the scenario where Cr exceeds the limit in seawater. The allowable amount of Cr entirely retained in sediments ranges from 0.69 to 47.2 kg/m2.In most scenarios, the accumulation of metals in sediments preferentially exceeds the corresponding threshold value rather than remaining in seawater. Therefore, we recommend using alkalization equipment to fully dissolve olivine before discharging into the sea, enabling a larger-scale application of olivine without significant negative ecological impacts.

Metal bioaccumulation and effects of olivine sand exposure on benthic marine invertebrates

Due to the anthropogenic increase of atmospheric CO2 emissions, humanity is facing the negative effects of rapid global climate change. Both active emission reduction and carbon dioxide removal (CDR) technologies are needed to meet the Paris Agreement and limit global warming to 1.5 °C by 2050. One promising CDR approach is coastal enhanced weathering (CEW), which involves the placement of sand composed of (ultra)mafic minerals like olivine in coastal zones. Although the large-scale placement of olivine sand could beneficially impact the planet through the consumption of atmospheric CO2 and reduction in ocean acidification, it may also have physical and geochemical impacts on benthic communities. The dissolution of olivine can release dissolved constituents such as trace metals that may affect marine organisms. Here we tested acute and chronic responses of marine invertebrates to olivine sand exposure, as well as examined metal accumulation in invertebrate tissue resulting from olivine dissolution. Two different ecotoxicological experiments were performed on a range of benthic marine invertebrates (amphipod, polychaete, bivalve). The first experiment included acute and chronic survival and growth tests (10 and 20 days, respectively) of olivine exposure while the second had longer (28 day) exposures to measure chronic survival and bioaccumulation of trace metals (e.g. Ni, Cr, Co) released during olivine sand dissolution. Across all fauna we observed no negative effects on acute survival or chronic growth resulting solely from olivine exposure. However, over 28 days of exposure, the bent-nosed clam Macoma nasuta experienced reduced burrowing and accumulated 4.2 ± 0.7 μg g ww-1 of Ni while the polychaete Alitta virens accumulated 3.5 ± 0.9 μg g ww-1 of Ni. No significant accumulation of any other metals was observed. Future work should include longer-term laboratory studies as well as CEW field studies to validate these findings under real-world scenarios.

Olivine avoidance behaviour by marine gastropods (Littorina littorea L.) and amphipods (Gammarus locusta L.) within the context of ocean alkalinity enhancement

Gigaton scale atmospheric carbon dioxide (CO2) 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 CO2 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).