Compensatory shell thickening in corrosive environments varies between related rocky-shore and estuarine gastropods.

Few studies have considered the capabilities of gastropods living in minerally-deficient acidified coastal waters to compensate for outer shell corrosion or compromised growing edge shell production. We compared inner shell thickening between pristine shells (control) and corroded shells (experiment) of two related intertidal neritid gastropod species from reduced salinity and acidified environments. We predicted that the rocky-shore, Nerita chamaeleon, which has greater access to shell building biomineralization substrates, should better control shell thickness than the estuarine, Neripteron violaceum. Accordingly, N. chameleon was found to compensate perfectly for variation in the thickness of the outer calcitic blocky layer (BL). Optimal shell thickness (OST) was maintained by selective reabsorption of the aperture ridge of the distal shell (aragonitic crossed-lamellar layer, CL) and by increased internal deposition of proximal (older) shell (aragonitic protocrossed lamellar, PCL). Despite greater exposure to acidification and hyposalinity, N. violaceum showed no significant compensatory shell thickening. These findings reveal that shell thickening capability may vary greatly among intertidal gastropods and that this may be constrained by environmental biomineralization substrate availability. Such environmentally-related responses carry implications for predicted future reductions in coastal water pH and salinity.

Noble metal catalyst detection in rocks using machine-learning: The future to low-cost, green energy materials?

Carbon capture and catalytic conversion to methane is promising for carbon-neutral energy production. Precious metals catalysts are highly efficient; yet they have several significant drawbacks including high cost, scarcity, environmental impact from the mining and intense processing requirements. Previous experimental studies and the current analytical work show that refractory grade chromitites (chromium rich rocks with Al2O3 > 20% and Cr2O3 + Al2O3 > 60%) with certain noble metal concentrations (i.e., Ir: 17-45 ppb, Ru: 73-178 ppb) catalyse Sabatier reactions and produce abiotic methane; a process which has not been investigated at the industrial scale. Thus, a natural source (chromitites) hosting noble metals might be used instead of concentrating noble metals for catalysis. Stochastic machine-learning algorithms show that among the various phases, the noble metal alloys are natural methanation catalysts. Such alloys form when pre-existing platinum group minerals (PGM) are chemically destructed. Chemical destruction of existing PGM results to mass loss forming locally a nano-porous surface. The chromium-rich spinel phases, hosting the PGM inclusions, are subsequently a second-tier support. The current work is the first multi-disciplinary research showing that noble metal alloys within chromium-rich rocks are double-supported, Sabatier catalysts. Thus, such sources could be a promising material in the search of low-cost, sustainable materials for green energy production.

Environmental radioactivity assessment of the Brunei Darussalam coastline of the South China Sea.

Radioactivity levels of naturally occurring radionuclides at the coast of Brunei Darussalam were evaluated along with their dose rates. Twenty-six berm and intertidal sediment samples were measured using gamma-ray spectrometry. The mean activity concentrations of 226Ra, 232Th and 40K in berm sediments were 10.07 ± 1.02 Bq/kg, below the minimum detectable activity, and 21.44 ± 1.23 Bq/kg, respectively, whereas for intertidal sediments they were 7.01 ± 0.87, 1.67 ± 0.15 and 4.99 ± 0.42 Bq/kg, respectively. With respect to the radiological health risk, the average hazard indices, absorbed gamma dose rate, effective dose equivalent, and excess lifetime cancer risk were found to be less than the global average. Calculation of the activity ratio showed that 40K is the main source of radiation in the coastal sediments. Furthermore, the difference in radioactivity levels between the berm sediments and intertidal sediments collected at the same location was investigated. Finally, a standard geological terminology of the littoral zone profile is proposed for describing coastal samples for universal communication among researchers.

Clay-shielded estuarine gastropods are better protected against environmental acidification than unshielded individuals.

The effects of progressive global acidification on the shells of marine organisms is a topic of much current interest. Most studies on molluscan shell resistance to dissolution consider the carbonate mineral component, with less known about the protective role of the outer organic periostracum. Outer-shell resistance would seem especially important to gastropods living in carbonate-undersaturated and calcium-deficient estuarine waters that threaten shell dissolution and constrain CaCO3 production. We tested this prediction using gastropods from an acidified estuarine population (Neripteron violaceum) that form a clay shield outside the periostracum. Specifically, we aimed to show that the carbonate shell component lacks integrity, that the formation of the clay shield is directed by the organism, and that the clay shield functions to protect against shell dissolution. We found no evidence for any specific carbonate dissolution resistance strategy in the thin, predominantly aragonitic shells of these gastropods. Shield formation was directed by an ornamented periostracum which strongly bonded illite elements (e.g., Fe, Al and S), that become available through suspension in the water column. In unshielded individuals, CaCO3 erosion was initiated randomly across the shell (not age-related) and progressed rapidly when the periostracum was breached. A light reflectance technique showed qualitatively that shield consolidation is negatively-related to shell erosion. These findings support a conceptual framework for gastropod outer-shell responses to acidification that considers both environmental and evolutionary constraints on shell construction. We describe a novel strategy for shell protection against dissolution, highlighting the diversity of mechanisms available to gastropods facing extreme coastal acidification.

Assessment of radioactivity concentration in intertidal sediments from coastal provinces in Oman and estimation of hazard and radiation indices.

The natural radioactivity of intertidal sediment samples collected from the beaches of Oman was investigated. Using gamma ray spectrometry, the activity concentrations of 226Ra, 232Th and 40K in the sediment samples were measured to have average values of 20.49 ± 3.50, 2.26 ± 0.60 and 44.83 ± 4.60 Bq kg-1 respectively. The activity levels reported are considerably lower than the worldwide average. The annual effective dose rate was estimated to be 0.015 mSv yr-1 on average. Additionally, the mean radium equivalent, external and internal indices were 26.89, 0.07 and 0.13 Bq kg-1 respectively which were well below the risk limits. Gamma and alpha radiation indices were computed to be less than unity and show no exceedance beyond the recommended level. Our results provide baseline data for radioactivity in intertidal sediment samples of Oman and show that intertidal beach sand does not pose significant radiological risk to human health.