The rise of preprints in earth sciences.

The rate of science information's spread has accelerated in recent years. In this context, it appears that many scientific disciplines are beginning to recognize the value and possibility of sharing open access (OA) online manuscripts in their preprint form. Preprints are academic papers that are published but have not yet been evaluated by peers. They have existed in research at least since the 1960s and the creation of ArXiv in physics and mathematics. Since then, preprint platforms-which can be publisher- or community-driven, profit or not for profit, and based on proprietary or free and open source software-have gained popularity in many fields (for example, bioRxiv for the biological sciences). Today, there are many platforms that are either disciplinary-specific or cross-domain, with exponential development over the past ten years. Preprints as a whole still make up a very small portion of scholarly publishing, but a large group of early adopters are testing out these value-adding tools across a much wider range of disciplines than in the past. In this opinion article, we provide perspective on the three main options available for earth scientists, namely EarthArXiv, ESSOAr/ESS Open Archive and EGUsphere.

Sorption vs adsorption: The words they are a-changin', not the phenomena.

In this discussion, we highlight that the terms sorption and adsorption are often confused and misused in many articles. Even if one thought their formal definition is well known, this does not appear to be the case. We recommend encouragement to adopt the word adsorption only when fully supported by appropriate data and using the sorption terminology when it is more speculative, typically in complex solid/fluid natural systems.

Effect of substrate properties and phosphorus supply on facilitating the uptake of rare earth elements (REE) in mixed culture cropping systems of Hordeum vulgare, Lupinus albus and Lupinus angustifolius.

This study presents how phosphate (P) availability and intercropping may influence the migration of rare earth elements (REEs) in legume-grass associations. In a replacement model, Hordeum vulgare was intercropped with 11% Lupinus albus and 11% Lupinus angustifolius. They were cultivated on two substrates, A (pH = 7.8) and B (pH = 6.6), and treated with 1.5 g P m-2 or 3 g P m-2. Simultaneously, a greenhouse experiment was conducted to quantify carboxylate release. There, one group of L. albus and L. angustifolius was supplied with either 200 µmol L-1 P or 20 µmol L-1 P. L. albus released higher amounts of carboxylates at low P supply than L. angustifolius, while L. angustifolius showed the opposite response. Plants cultivated on substrate B accumulated substantially higher amounts of nutrients and REE, compared to substrate A. Higher P supply did not influence the leaf and stem P concentrations of H. vulgare. Addition of P decreased REE accumulation in barley monocultures on alkaline soil A. However, when H. vulgare was cultivated in mixed culture with L. angustifolius on alkaline substrate A with high P supply, the accumulation of REE in H. vulgare significantly increased. Conversely, on acidic substrate B, intercropping with L. albus decreased REE accumulation in H. vulgare. Our findings suggest a predominant effect of soil properties on the soil-plant transfer of REEs. However, in plant communities and within a certain soil environment, interspecific root interactions determined by species-specific strategies related to P acquisition in concert with the plant's nutrient supply impact REE fluxes between neighbouring plants.

Geochemical signatures of rare earth elements and yttrium exploited by acid solution mining around an ion-adsorption type deposit: Role of source control and potential for recovery.

Elevated concentrations of rare earth elements and yttrium (REE + Y) in acid mine drainage (AMD) attract worldwide attention. However, the source and control of REE + Y distribution patterns in AMD remain unclear. Water, rock, sediment, and sludge samples were collected from an ion-adsorption deposit site to investigate REE + Y concentrations and distributions. The heavy REE (HREE)-enriched patterns of the AMD resulted from preferential desorption of HREE in the clay-rich sediment strata, from which the REE + Y were ion-exchanged by an in-situ underground leaching process using ammonium sulfate brine. Free ions and sulfate complexes preserved REE + Y patterns and facilitated REE + Y mobility in the AMD leachate system. High concentrations of REE + Y occurred in the AMD, and decreased progressively through nitrification-denitrification and coagulation-precipitation procedures in a water treatment plant. Concentrations of REE + Y were one to three orders of magnitude higher in AMD than those in groundwater, and were negatively correlated (r2 = -0.72) with pH (3.8 to 8.7), suggesting that an acid desorption from minerals contributed the REE + Y to the AMD from the source rock. Normalized REE + Y patterns showed enrichments of HREE over light REE (LREE) and negative Ce anomaly. The distribution patterns were relatively constant for all water samples, despite their huge difference in REE + Y concentrations. This suggested a limited impact of preferential precipitation of LREE over HREE on REE + Y fractionations during neutralization. The potentially recoverable LREE and HREE were calculated to range between 1.12 kg/day and 3.37 kg/day, and between 1.29 kg/day and 3.76 kg/day, respectively. The findings reported in this study lend promise for efficient REE + Y recovery from AMD.

Open Access publishing practice in geochemistry: overview of current state and look to the future.

Open Access (OA) describes the free, unrestricted access to and re-use of research articles. Recently, a new wave of interest, debate, and practice surrounding OA publishing has emerged. In this paper, we provide a simple overview of the trends in OA practice in the broad field of geochemistry. Characteristics of the approach such as whether or not an article processing charge (APC) exists, what embargo periods or restrictions on self-archiving' policies are in place, and whether or not the sharing of preprints is permitted are described. The majority of journals have self-archiving policies that allow authors to share their peer reviewed work via green OA without charge. There is no clear relationship between journal impact and APC. The journals with the highest APC are typically those of the major commercial publishers, rather than the geochemistry community themselves. The rise in OA publishing has potential impacts on the profiles of researchers and tends to devolve costs from organizations to individuals. Until the geochemistry community makes the decision to move away from journal-based evaluation criteria, it is likely that such high costs will continue to impose financial inequities upon research community. However, geochemists could more widely choose legal self-archiving as an equitable and sustainable way to disseminate their research.

Comments on "Factors affecting global flow of scientific knowledge in environmental sciences" by Sonne et al. (2020).

There are major challenges that need to be addressed in the world of scholarly communication, especially in the field of environmental studies and in the context of the United Nations Sustainable Development Goals. Recently, Sonne et al. (2020) published an article in Science of the Total Environment discussing some of these challenges. However, we feel that many of the arguments misrepresent critical elements of Open Access (OA), Plan S, and broader issues in scholarly publishing. In our response, we focus on addressing key elements of their discussion on (i) OA and Plan S, as well as (ii) Open Access Predatory Journals (OAPJ). The authors describe OA and Plan S as restricting author choice, especially through the payment of article-processing charges. The reality is that 'green OA' self-archiving options alleviate virtually all of the risks they mention, and are even the preferred 'routes' to OA as stated by both institutional and national policies in Denmark. In alignment with this, Plan S is also taking a progressive stance on reforming research evaluation. The assumptions these authors make about OA in the "global south" also largely fail to acknowledge some of the progressive work being done in regions like Indonesia and Latin America. Finally, Sonne et al. (2020) highlight the threat that OAPJs face to our scholarly knowledge production system. While we agree generally that OAPJs are problematic, the authors simultaneously fail to mention many of the excellent initiatives helping to combat this threat (e.g., the Directory of Open Access Journals). We call for researchers to more effectively equip themselves with sufficient knowledge of relevant systems before making public statements about them, in order to prevent misinformation from polluting the debate about the future of scholarly communication.

On the difficulties of being rigorous in environmental geochemistry studies: some recommendations for designing an impactful paper.

There have been numerous environmental geochemistry studies using chemical, geological, ecological, and toxicological methods but each of these fields requires more subject specialist rigour than has generally been applied so far. Field-specific terminology has been misused and the resulting interpretations rendered inaccurate. In this paper, we propose a series of suggestions, based on our experience as teachers, researchers, reviewers, and editorial board members, to help authors to avoid pitfalls. Many scientific inaccuracies continue to be unchecked and are repeatedly republished by the scientific community. These recommendations should help our colleagues and editorial board members, as well as reviewers, to avoid the numerous inaccuracies and misconceptions currently in circulation and establish a trend towards greater rigour in scientific writing.

It's Time to Replace the Term "Heavy Metals" with "Potentially Toxic Elements" When Reporting Environmental Research.

Even if the Periodic Table of Chemical Elements is relatively well defined, some controversial terms are still in use. Indeed, the term "heavy metal" is a common term used for decades in the natural sciences, and even more in environmental sciences, particularly in studies of pollution impacts. As the use of the term appears to have increased, we highlight the relevance of the use of the term "Potentially Toxic Element(s)", which needs more explicit endorsement, and we illustrate the chemical elements that need to be considered.

Behavior of rare earth elements in an aquifer perturbed by CO2 injection: Environmental implications.

Three cubic-meters of CO2-saturated water was injected into a subsurface fractured aquifer in a post-mined area, using a push-pull test protocol. Groundwater samples were collected before and after CO2-injection to quantify geochemical changes. CO2-injection initially reduced the pH of water from 7.3 to 5.7, led to the enrichment of major ions (Ca2+, Mg2+, and alkalinity), and dissolved trace metals (including Fe, Mn, As, and Zn) in the groundwater. Rare earth elements (REE) and yttrium concentrations were also measured in these samples before and after CO2 perturbation, to evaluate their behavior. An enrichment of total Y plus REE (REY) occurred. REY fractionation was observed with higher heavy REE (HREE) enrichment compared to light REE (LREE), and significant variations in La/Yb and Y/Ho ratios were observed following CO2 perturbation. Enrichment by a factor of three was observed for Y, Lu, and Tm, and by nearly one order of magnitude for Dy and Yb. A geochemical model was used to evaluate the amount of REE aqueous ions complexed throughout the experiment. Modeling of the results showed that speciation of dissolved REE with carbonate, along with desorption from iron oxyhydroxide surface were the main factors controlling REE behavior. This study increases an understanding of dissolved REE behavior in the environment, and the potential use for applying iron oxides for REE recovery from mine drainages. Furthermore, the description of REE fractionation patterns may assist in surveying CO2 geological storage sites, surveying underground waste disposal sites, and for understanding the formation of ore deposits and fluid inclusions in geological formations.

Role of Manganese Oxyhydroxides in the Transport of Rare Earth Elements Along a Groundwater Flow Path.

Rare earth elements (REE) are known to be emerging contaminants in hydrosphere, but roles of hydrous manganese oxyhydroxides (HMO) in REE transport in groundwater remains unknown. In this study, groundwater was sampled along a flow path in the North China Plain to determine the behavior of REE surface complexation to HMO by a modeling and field study approach. Results show that the proportion of neodymium (Nd) complexed by HMO ranges from 0.2% to 95.8%, and from 0.3% to 99.6% in shallow groundwater and deep groundwater, respectively. The amount of complexed REE increases along the flow path. REE bound to HMO exhibit decreasing trends with increasing atomic number. The process was determined to be independent of pH, HMO content, and metal loading. This finding further demonstrates HMO-REE complexation plays a key role in transport of REE in groundwater through preferential scavenging of light REE (LREE) over heavy REE (HREE). Nevertheless, carbonate ligands appear to be robust competitors in reducing the amount of REE sorbed to HMO when solution pH rises above 8.0. Assuming that 50% of Mn concentration occurs as HMO, the amount of complexed REE was predicted to show a more marked decrease in LREE compared to that of HREE.

Impact of Hydrous Manganese and Ferric Oxides on the Behavior of Aqueous Rare Earth Elements (REE): Evidence from a Modeling Approach and Implication for the Sink of REE.

In this study, models were used for the first time to investigate the fate and transport of rare earth elements (REE) in the presence of hydrous manganese and ferric oxides in groundwaters from the coastal Bohai Bay (China). Results showed that REE sorption is strongly dependent on pH, as well as hydrous manganese and ferric oxide content. Higher proportions of REE were sorbed by hydrous manganese oxide as compared to hydrous ferric oxides, for example in the presence of neodymium. In this case, a mean 28% of this element was sorbed by hydrous manganese oxide, whereas an average 7% sorption was observed with hydrous ferric oxides. A contrasting REE sorption behavior was observed with hydrous manganese and ferric oxide for all investigated groundwaters. Specifically, REE bound to hydrous manganese oxides showed decreasing sorption patterns with increasing atomic number. The opposite trend was observed in the presence of hydrous ferric oxides. In addition, these results suggested that light REE (from La to Sm) rather than heavy REE (from Eu to Lu) are preferentially scavenged by hydrous manganese oxide. However, the heavy REE showed a greater affinity for hydrous ferric oxides compared to light REE. Therefore, both hydrous manganese and ferric oxide are important scavengers of REE. This study shows the implication of hydrous manganese and ferric oxide sorption for the sink of REE in groundwater.

Characterization of metal binding sites onto biochar using rare earth elements as a fingerprint.

The ability of biochar to immobilize metals relies on the amount of functional groups at its surface but the contribution of each functional groups (e.g. carboxylic, phenolic) to metal bonding is poorly known. Using a new approach based on previous works on rare earth element (REE) interactions with humic substances, we aim at elucidating the relative contribution of these binding sites to metal sorption under various conditions (i.e. pH and ionic strengths, IS). Using batch experiments, REE sorption onto biochar was analyzed from pH 3 to 9 and IS 10-1 mol/L to 10-3 mol/L. Rare earth element patterns show a Middle REE (MREE) downward concavity at acidic pH and low ionic strength. These patterns are in good agreement with existing datasets quantifying REE binding with humic substances. Indeed, the MREE downward concavity displayed by REE-biochar complexation pattern compares well with REE patterns with various organic compounds. This similarity in the REE complexation pattern shapes suggests that carboxylic groups are the main binding sites of REE in biochar. Overall, our results indicate that the strength of the metal bonding with biochar increases when pH and IS increase, suggesting that biochar is more efficient for long-term metal immobilization at near neutral pH and high ionic strength.

Aqueous chemistry of Ce(iv): estimations using actinide analogues.

The prediction of cerium (Ce) aqueous speciation is relevant in many research fields. Indeed, Ce compounds are used for many industrial applications, which may require the control of Ce aqueous chemistry for their synthesis. The aquatic geochemistry of Ce is also of interest. Due to its growing industrial use and its release into the environment, Ce is now considered as an emerging contaminant. Cerium is also used as a proxy of (paleo)redox conditions due to the Ce(iv)/Ce(iii) redox transition. Finally, Ce(iv) is often presented as a relevant analogue of tetravalent actinides (An(iv)). In the present study, quantum chemical calculations were conducted to highlight the similarities between the structures of Ce(iv) and tetravalent actinide (An(iv); An = Th, Pa, U, Np, Pu) aqua-ions, especially Pu(iv). The current knowledge of An(iv) hydrolysis, solubility and colloid formation in water was briefly reviewed but important discrepancies were observed in the available data for Ce(iv). Therefore, new estimations of the hydrolysis constants of Ce(iv) and the solubility of Ce(iv)-(hydr)oxides are proposed, by analogy with Pu(iv). By plotting pH-Eh (Pourbaix) diagrams, we showed that the pH values corresponding to the onset of Ce(iv) species formation (i.e. Ce(iv)-(hydr)oxide or dissolved Ce(iv)) agreed with various experimental results. Although further experimental studies are required to obtain a more accurate thermodynamic database, the present work might yet help to predict more accurately the Ce chemical behavior in aqueous solution.

Continental shelves as potential resource of rare earth elements.

The results of this study allow the reassessment of the rare earth elements (REE) external cycle. Indeed, the river input to the oceans has relatively flat REE patterns without cerium (Ce) anomalies, whereas oceanic REE patterns exhibit strong negative Ce anomalies and heavy REE enrichment. Indeed, the processes at the origin of seawater REE patterns are commonly thought to occur within the ocean masses themselves. However, the results from the present study illustrate that seawater-like REE patterns already occur in the truly dissolved pool of river input. This leads us to favor a partial or complete removal of the colloidal REE pool during estuarine mixing by coagulation, as previously shown for dissolved humic acids and iron. In this latter case, REE fractionation occurs because colloidal and truly dissolved pools have different REE patterns. Thus, the REE patterns of seawater could be the combination of both intra-oceanic and riverine processes. In this study, we show that the Atlantic continental shelves could be considered potential REE traps, suggesting further that shelf sediments could potentially become a resource for REE, similar to metalliferous deep sea sediments.

Copper and cobalt accumulation in plants: a critical assessment of the current state of knowledge.

This review synthesizes contemporary understanding of copper-cobalt (Cu-Co) tolerance and accumulation in plants. Accumulation of foliar Cu and Co to > 300 µg g-1 is exceptionally rare globally, and known principally from the Copperbelt of Central Africa. Cobalt accumulation is also observed in a limited number of nickel (Ni) hyperaccumulator plants occurring on ultramafic soils around the world. None of the putative Cu or Co hyperaccumulator plants appears to comply with the fundamental principle of hyperaccumulation, as foliar Cu-Co accumulation is strongly dose-dependent. Abnormally high plant tissue Cu concentrations occur only when plants are exposed to high soil Cu with a low root to shoot translocation factor. Most Cu-tolerant plants are Excluders sensu Baker and therefore setting nominal threshold values for Cu hyperaccumulation is not informative. Abnormal accumulation of Co occurs under similar circumstances in the Copperbelt of Central Africa as well as sporadically in Ni hyperaccumulator plants on ultramafic soils; however, Co-tolerant plants behave physiologically as Indicators sensu Baker. Practical application of Cu-Co accumulator plants in phytomining is limited due to their dose-dependent accumulation characteristics, although for Co field trials may be warranted on highly Co-contaminated mineral wastes because of its relatively high metal value.

Lead distribution in soils impacted by a secondary lead smelter: Experimental and modelling approaches.

Smelting activities are one of the most common sources of trace elements in the environment. The aim of this study was to determine the lead distribution in upper horizons (0-5 and 5-10cm) of acidic soils in the vicinity of a lead-acid battery recycling plant in northern France. The combination of chemical methods (sequential extractions), physical methods (Raman microspectroscopy and scanning electron microscopy with an energy dispersive spectrometer) and multi-surface complexation modelling enabled an assessment of the behaviour of Pb. Regardless of the studied soil, none of the Pb-bearing phases commonly identified in similarly polluted environments (e.g., anglesite) were observed. Lead was mainly associated with organic matter and manganese oxides. The association of Pb with these soil constituents can be interpreted as evidence of Pb redistribution in the studied soils following smelter particle deposition.