Modeling diffusive Cd and Zn contaminant emissions from soils to surface waters

Climate Change Implications for Metal and Metalloid Dynamics in Aquatic Ecosystems and its Context within the Decade of Ocean Sciences

Anthropogenic activities are affecting marine ecosystems, notably coastal ones, in multiple ways and at increasing rates, leading to habitat degradation, loss of biodiversity, and greater exposure of flora and fauna to chemical contaminants, with serious effects on ocean health. Chemical pollution, in particular, is a significant negative stressor for aquatic ecosystems, both oceanic and coastal, and has recently been identified as a priority for conservation efforts. Metals and metalloids, in particular, present environmental persistence, bioavailability, tendency to bioaccumulate along the trophic chain, and potential toxic effects. However, the current scenario of climate change is increasingly affecting the aquatic environment, altering water mass flows and the transport of pollutants, aggravating toxic effects and ecological risks. Moreover, although traditional sources of contamination have been studied for decades, many knowledge gaps persist, in addition to the emerging effects of climate change that are still poorly studied. In this regard, this review aims to discuss climate change implications for metal and metalloid dynamics in aquatic ecosystems and its context within the Decade of Ocean Sciences. We also discuss how an increasing interest in plastic pollution has led to contamination by metals and metalloids being neglected, requiring mutual efforts to move forward in the understating of the negative and often lethal impacts of this type of pollutants, thus aiming at prioritizing contamination by metals and metalloids not just in the oceans, but in all water bodies.

Thinking for the future: Phytoextraction of cadmium using primed plants for sustainable soil clean-up

Cadmium (Cd) soil contamination is a global problem for food security due to its ubiquity, toxicity at low levels, persistence, and bioaccumulation in living organisms. Humans' intake of heavy metals is usually due to direct contact with contaminated soil, through the food chain (Cd accumulation in crops and edible plants) or through drinking water in cases of coupled groundwater-surface water systems. Phytoextraction is one of the eco-friendly, sustainable solutions that can be used as a method for soil clean-up with the possibility of re-use of extracted metals through phytomining. Phytoextraction is often limited by the tolerance level of hyperaccumulating plants and the restriction of their growth. Mechanisms of hyperaccumulation of heavy metals in tolerant species have been studied, but there are almost no data on mechanisms of further improvement of the accumulation capacity of such plants. Priming can influence plant stress tolerance by the initiation of mild stress cues resulting in acclimation of the plant. The potential of plant priming in abiotic stress tolerance has been extensively investigated using different types of molecules that are supplemented exogenously to plant organs (roots, leaves, etc.), resulting in enhanced tolerance of abiotic stress. This review focuses on mechanisms of enhancement of plant stress tolerance in hyperaccumulating plants for their exploitation in phytoextraction processes.

Projecting impacts of climate change on metal mobilization at contaminated sites: Controls by the groundwater level

Heavy metal and metalloid contamination of topsoils from atmospheric deposition and release from landfills, agriculture, and industries is a widespread problem that is estimated to affect >50% of the EU's land surface. Influx of contaminants from soil to groundwater and their further downstream spread and impact on drinking water quality constitute a main exposure risk to humans. There is increasing concern that the present contaminant loading of groundwater and surface water systems may be altered, and potentially aggravated, by ongoing climate change, through large-scale impacts on recharge and groundwater levels. We investigated this issue by performing hydrogeological-geochemical model projections of changes in metal(loid) (As and Pb) mobilization in response to possible (climate-driven) future shifts in groundwater level and fluctuation amplitudes. We used observed initial conditions and boundary conditions for contaminated soils in the temperate climate zone. The results showed that relatively modest increases (0.2 m) in average levels of shallow groundwater systems, which may occur in Northern Europe within the coming two decades, can increase mass flows of metals through groundwater by a factor of 2-10. There is a similar risk of increased metal mobilization in regions subject to increased (seasonal or event-scale) amplitude of groundwater levels fluctuations. Neglecting groundwater level dynamics in predictive models can thus lead to considerable and systematic underestimation of metal mobilization and future changes. More generally, our results suggest that the key to quantifying impacts of climate change on metal mobilization is to understand how the contact between groundwater and the highly water-conducting and geochemically heterogeneous topsoil layers will change in the future.

The Impact of Climate Change on Metal Transport in a Lowland Catchment

This study investigates the impact of future climate change on heavy metal (i.e., Cd and Zn) transport from soils to surface waters in a contaminated lowland catchment. The WALRUS hydrological model is employed in a semi-distributed manner to simulate current and future hydrological fluxes in the Dommel catchment in the Netherlands. The model is forced with climate change projections and the simulated fluxes are used as input to a metal transport model that simulates heavy metal concentrations and loads in quickflow and baseflow pathways. Metal transport is simulated under baseline climate ("2000-2010") and future climate ("2090-2099") conditions including scenarios for no climate change and climate change. The outcomes show an increase in Cd and Zn loads and the mean flux-weighted Cd and Zn concentrations in the discharged runoff, which is attributed to breakthrough of heavy metals from the soil system. Due to climate change, runoff enhances and leaching is accelerated, resulting in enhanced Cd and Zn loads. Mean flux-weighted concentrations in the discharged runoff increase during early summer and decrease during late summer and early autumn under the most extreme scenario of climate change. The results of this study provide improved understanding on the processes responsible for future changes in heavy metal contamination in lowland catchments.