Sulphur isotopes as tracers of the influence of potash mining in groundwater salinisation in the Llobregat Basin (NE Spain)

Unraveling the molecular mechanisms of fish physiological response to freshwater salinization: A comparative multi-tissue transcriptomic study in a river polluted by potash mining

Freshwater salinization is an escalating global environmental issue that threatens freshwater biodiversity, especially fish populations. This study aims to uncover the molecular basis of salinity physiological responses in a non-native minnow species (Phoxinus septimaniae x P. dragarum) exposed to saline effluents from potash mines in the Llobregat River, Barcelona, Spain. Employing high-throughput mRNA sequencing and differential gene expression analyses, brain, gills, and liver tissues collected from fish at two stations (upstream and downstream of saline effluent discharge) were examined. Salinization markedly influenced global gene expression profiles, with the brain exhibiting the most differentially expressed genes, emphasizing its unique sensitivity to salinity fluctuations. Pathway analyses revealed the expected enrichment of ion transport and osmoregulation pathways across all tissues. Furthermore, tissue-specific pathways associated with stress, reproduction, growth, immune responses, methylation, and neurological development were identified in the context of salinization. Rigorous validation of RNA-seq data through quantitative PCR (qPCR) underscored the robustness and consistency of our findings across platforms. This investigation unveils intricate molecular mechanisms steering salinity physiological response in non-native minnows confronting diverse environmental stressors. This comprehensive analysis sheds light on the underlying genetic and physiological mechanisms governing fish physiological response in salinity-stressed environments, offering essential knowledge for the conservation and management of freshwater ecosystems facing salinization.

Disentangling sources and transformation mechanisms of nitrogen, sulfate, and carbon in water of a Karst Critical Zone

In the Karst Critical Zone (KCZ), mining and urbanization activities produce multiple pollutants, posing a threat to the vital groundwater and surface water resources essential for drinking and irrigation. Despite their importance, the interactions between these pollutants in the intricate hydrology and land use of the KCZ remain poorly understood. In this study, we unraveled the transformation mechanisms and sources of nitrogen, sulfate, and carbon using multiple isotopes and the MixSIAR model, following hydrology and surface analyses conducted in spatial modelling with ArcGIS. Our results revealed frequent exchange between groundwater and surface water, as evidenced by the analysis of δD-H2O and δ18O-H2O. Nitrification predominantly occurred in surface water, although denitrification also made a minor contribution. Inorganic nitrogen in both groundwater and surface water primarily originated from soil nitrogen (48 % and 49 %, respectively). Sewage and manure were secondary sources of inorganic nitrogen in surface water, accounting for 41 % in urban and 38 % in mining areas. Notably, inorganic sulfur oxidation displayed significant spatial disparities between urban and mining areas, rendering groundwater more susceptible to sulfur pollution compared to surface water. The frequent interchange between groundwater and surface water posed a higher pollution risk to groundwater. Furthermore, the primary sources of CO2 and HCO3- in both groundwater and surface water were water‑carbonate reactions and soil respiration. Sulfide oxidation was found to enhance carbonate dissolution, leading to increased CO2 release from carbonate dissolution in the KCZ. These findings enhance our understanding of the transformation mechanisms and interactions of nitrogen, sulfur, and carbon in groundwater and surface water. This knowledge is invaluable for accurately controlling and treating water pollution in the KCZ.

Characterization and health risk assessment of arsenic in natural waters of the Indus River Basin, Pakistan

The elevated concentrations of arsenic in natural water are one of the major environmental threats to human health. However, the existing characteristics, controlling mechanisms, and associated risks of arsenic in natural waters in the Indus River Basin (IRB), Pakistan, are yet to be unequivocally understood. In this study, a total of 203 samples of surface water (SW), shallow groundwater (SGW), and deep groundwater (DGW) were collected from the IRB to assess the geochemical characteristics of arsenic and its associated health risks, as all three kinds of waters are the main sources of drinking and domestic usage. The results revealed that the arsenic concentrations in the SW, SGW, and DGW were in the ranges of 1.1-26.45, 1.05-44.44, and 0.67-41.09 μg L^-1, respectively. Furthermore, the predominance of As (V) (97 %) over As(III) (3 %) confirmed that the desorption of As in oxidizing environments with elevated pH and Eh is the controlling mechanism. The hazard quotient of 11-45 % and 20-60 % samples and cancer risk of 26-64 % and 26-68 % samples indicated high health risks for the adults and children, respectively, suggesting an immense need for appropriate measures of reducing natural water arsenic concentrations in IRB from the human health perspectives.

Origins of Sulfate in Groundwater and Surface Water of the Rio Grande Floodplain, Texas, USA and Chihuahua, Mexico

Sulfate isotopes (δ34S, δ18OSO4) interpreted in conjunction with sulfate concentrations show that sulfate of both agricultural and geologic sources is present in groundwater and surface water in the Rio Grande flood plain within the Hueco Bolsón. From previous studies, water isotopes (δ2H, δ18O) in the study area indicate groundwater age relative to dam construction upstream. Surface water entering the Hueco Bolsón contains a mixture of soil-amendment sulfate and sulfate from deep-basin groundwater seeps at the terminus of Mesilla Valley. In the shallow Rio Grande alluvial aquifer within the Hueco Bolsón, ranges of δ34S in pre-dam (+2 to +9‰) and post-dam (0 to +6‰) groundwater overlap; the range for post-dam water coincides with common high-sulfate soil amendments used in the area. Most post-dam groundwater, including discharge into agricultural drains, has higher sulfate than pre-dam groundwater. In surface water downstream of Fabens, high-δ34S (>+10‰) sulfate, resembling Middle Permian gypsum, mixes with sulfate from upstream sources and agriculture. The high- δ34S sulfate probably represents discharge from the regional Hueco Bolsón aquifer. In surface water downstream of Fort Hancock, soil-amendment sulfate predominates, probably representing discharge from the Rio Grande alluvial aquifer near the basin terminus. The δ18OSO4 dataset is consistent with sulfate origins determined from the larger δ34S dataset.

Multiple stable isotopes and geochemical approaches to elucidate groundwater salinity and contamination in the critical coastal zone: A case from the Bou-areg and Gareb aquifers (North-Eastern Morocco)

Mediterranean areas are characterized by complex hydrogeological systems, where water resources are faced with several issues such as salinity and pollution. Fifty-one water samples were gathered from the Bou-areg coastal and the Gareb aquifers to evaluate the source of water salinity and to reveal the processes of the different sources of pollution using a variety of chemical and isotopic indicators (δ²H-H2O, δ¹⁸O-H2O, δ³⁴S-SO4, and δ¹⁸O-SO4). The results of the hydrochemical analysis of water samples show that the order of dominated elements is Cl^- > HCO₃^- > SO4₂^- > NO₃^- and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and evidenced extremely high salinity levels (EC up to 22000 μS/cm). All samples exceeded the WHO drinking water guidelines, making them unfit for human consumption. Ion ratio diagrams, isotopic results, and graphical comparing indicate that the mineralization of groundwater in the area, is controlled by carbonate dissolution, evaporite dissolution, ion exchange, and sewage invasion. The return of irrigation water plays a significant role as well in the groundwater recharge and its mineralization by fertilizers mainly. Evaporites (Gypsum), sewage, and fertilizers constitute the main sources of sulfates in the investigated water resources. These scientific results will be an added value for decision-makers to more improve the sustainable management of groundwater in water-stressed regions. The use of chemical and isotopic tracers once again shows their relevance in such zones where systematic monitoring is lacking.

A review of the distribution, sources, genesis, and environmental concerns of salinity in groundwater

Awareness concerning the degradation of groundwater quality and their exacerbating adverse effects due to salinization processes is gaining traction, raising for adequate understanding of the distribution, sources, genesis, and environmental concerns of salinity in groundwater. Saline groundwater is widely distributed all over the world, with an area of 24 million km² (16% of the total land area on earth) and 1.1 billion people living in the affected areas, especially the arid/semi-arid areas in developing countries. These large-scale groundwater salinization problems are sourced from two major ways: natural and anthropogenic. The natural sources are diversified from connate saline groundwater, seawater intrusion, evaporation, dissolution of soluble salts, membrane filtration process to geothermal origin. The anthropogenic sources include irrigation return flow, road deicing salts, industrial and agricultural wastewater, and gas and oil production activities. The integrated approach of geochemical tracers and multiple isotopes (δ¹⁸O_H2O, δ²H_H2O, δ¹¹B, δ³⁶Cl, δ³⁴S_sulfate, ⁸⁷Sr/⁸⁶Sr, and δ⁷Li) is proved to be useful in the constraints of the origin and transport of solutes in groundwater. Groundwater salinization is often associated with high levels of some toxic elements like arsenic, fluoride, selenium, and boron. Four "triggers" lead to this association: salt effect, competing adsorption, microbial processes, and cation exchange.

Research Advances in Identifying Sulfate Contamination Sources of Water Environment by Using Stable Isotopes

As the main anion of groundwater, the content of sulfate affects the drinking water safety and ecological security directly. In recent years, with the acceleration of industrialization and urbanization development, the problem of sulfate pollution in water environments is becoming more and more serious. It is critical to effectively identify the sulfate sources of water environment to ensure human health and the benign evolution of water environment. Due to its “fingerprints” feature, the sulfur and oxygen isotopes of SO₄²⁻ have been widely used to identify sources of sulfate contamination in water environment. However, research advances in tracing sulfate contamination sources of water environment by using stable isotopes are rarely reported. This paper reviewed the research advances of sulfate isotope technology domestically and abroad, which was used to trace the sources of sulfate pollution in water environment, compared different pre-treatment methods for analyzing the δ³⁴S and δ¹⁸O of sulfate, and compiled the ranges of typical values of δ³⁴S and δ¹⁸O from different potential sources of sulfate contamination. In this review, the limitation of the technique in traceability of sulfate pollution was also discussed, and the future traceability techniques of sulfate pollution were prospected.

Do all roads lead to Rome? Exploring community trajectories in response to anthropogenic salinization and dilution of rivers

Abiotic stress shapes how communities assemble and support ecological functions. However, it remains unclear whether artificially increasing or decreasing stress levels would lead to communities assembling predictably along a single axis of variation or along multiple context-dependent trajectories of change. In response to stress intensity alterations, we hypothesize that a single trajectory of change occurs when trait-based assembly prevails, while multiple trajectories of change arise when dispersal-related processes modify colonization and trait-filtering dynamics. Here, we tested these hypotheses using aquatic macroinvertebrates from rivers exposed to gradients of natural salinity and artificially diluted or salinized ion contents. Our results showed that trait-filtering was important in driving community assembly in natural and diluted rivers, while dispersal-related processes seemed to play a relevant role in response to salinization. Salinized rivers showed novel communities with different trait composition, while natural and diluted communities exhibited similar taxonomic and trait compositional patterns along the conductivity gradient. Our findings suggest that the artificial modification of chemical stressors can result in different biological communities, depending on the direction of the change (salinization or dilution), with trait-filtering, and organism dispersal and colonization dynamics having differential roles in community assembly. The approach presented here provides both empirical and conceptual insights that can help in anticipating the ecological effects of global change, especially for those stressors with both natural and anthropogenic origins.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Naturalizing pollution: a critical social science view on the link between potash mining and salinization in the Llobregat river basin, northeast Spain

The scientific literature distinguishes between primary or natural and secondary or human-induced salinization. Assessing this distinction is of vital importance to assign liabilities and responsibilities in pollution cases and for designing the best policy and management actions. In this context, actors interested in downplaying the role of certain drivers of human-induced salinization can attempt to neglect its importance by referring to natural salinization, in a similar fashion to other pollution and health-related cases, from tobacco smoke to climate change. Potash mining, which has experienced continued growth during the last decades and is a significant contributor to salinization, is prone to originate such controversies because natural salinization from the saline geological catch can be mixed with salinization produced by mining waste such as brines and mine tailings, thus obscuring the distinction between causes. By reviewing the long-standing social and environmental conflict caused by potash mining in a region of Mediterranean climate—the Llobregat river basin—in this article, we highlight the importance of the impacts of salinization on human health and provide a critical social science perspective on salinization processes.

This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Regulations are needed to protect freshwater ecosystems from salinization

Anthropogenic activities such as mining, agriculture and industrial wastes have increased the rate of salinization of freshwater ecosystems around the world. Despite the known and probable consequences of freshwater salinization, few consequential regulatory standards and management procedures exist. Current regulations are generally inadequate because they are regionally inconsistent, lack legal consequences and have few ion-specific standards. The lack of ion-specific standards is problematic, because each anthropogenic source of freshwater salinization is associated with a distinct set of ions that can present unique social and economic costs. Additionally, the environmental and toxicological consequences of freshwater salinization are often dependent on the occurrence, concentration and ratios of specific ions. Therefore, to protect fresh waters from continued salinization, discrete, ion-specific management and regulatory strategies should be considered for each source of freshwater salinization, using data from standardized, ion-specific monitoring practices. To develop comprehensive monitoring, regulatory, and management guidelines, we recommend the use of co-adaptive, multi-stakeholder approaches that balance environmental, social, and economic costs and benefits associated with freshwater salinization.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Effects of mining activities on evolution of water quality of karst waters in Midwestern Guizhou, China: evidences from hydrochemistry and isotopic composition

Zhijin coal-mining district, located in Midwestern Guizhou Province, has been extensively exploited for several decades. The discharge of acid mine drainage (AMD) has constituted a serious threat to local water environmental quality, which greatly affected the normal use of local people. The Permian limestone aquifer is the essential potable water supply for local people, which covered under the widely distributed coal seams. To investigate the origin of the water, the evolutionary processes, and the sources of dissolved sulfate in the karst waters, the mine water, surface water, and groundwater near the coal mines were sampled for stable isotopes (H, O, and S) and conventional hydrochemical analysis. The results of hydrochemistry and isotopic composition indicate that the regional surface water and partial karst groundwater are obviously affected by coal-mining activities, which is mainly manifested in the increase of water solute concentration and the change of hydrochemical types. The isotopic composition of δ²H_H2O and δ¹⁸O_H2O indicates that the major recharge source of surface water and the groundwater is atmospheric precipitation and that it is influenced obviously by evaporation in the recharge process. The surface water is mainly controlled by the oxidation of pyrite, as well as the dissolution of carbonate rocks, whereas that of natural karst waters is influenced by the dissolution of carbonate rocks. The resulting δ³⁴S_SO4 values suggest that the dissolved sulfate source in the surface water is mainly pyrite oxidation but atmospheric precipitation for the karst groundwater. Given the similar chemistry and isotopic composition between surface water and partial groundwater, it is reasonable to assume that most of the dissolved sulfate source in part of the groundwater was derived through the oxidation of pyrite in the coal. Furthermore, the contamination of the surface water and partial groundwater from the coal seam has occurred distinctly in the catchment, which is enriched in SO₄^2- and is mostly depleted δ³⁴S in sulfate.

Occurrence of chemical contaminants in peri-urban agricultural irrigation waters and assessment of their phytotoxicity and crop productivity

Water scarcity and water pollution have increased the pressure on water resources worldwide. This pressure is particularly important in highly populated areas where water demand exceeds the available natural resources. In this regard, water reuse has emerged as an excellent water source alternative for peri-urban agriculture. Nevertheless, it must cope with the occurrence of chemical contaminants, ranging from trace elements (TEs) to organic microcontaminants. In this study, chemical contaminants (i.e., 15 TEs, 34 contaminants of emerging concern (CECs)), bulk parameters, and nutrients from irrigation waters and crop productivity (Lycopersicon esculentum Mill. cv. Bodar and Lactuca sativa L. cv. Batavia) were seasonally surveyed in 4 farm plots in the peri-urban area of the city of Barcelona. A pristine site, where rain-groundwater is used for irrigation, was selected for background concentrations. The average concentration levels of TEs and CECs in the irrigation water impacted by treated wastewater (TWW) were 3 (35±75μgL^-1) and 13 (553±1050ngL^-1) times higher than at the pristine site respectively. Principal component analysis was used to classify the irrigation waters by chemical composition. To assess the impact of the occurrence of these contaminants on agriculture, a seed germination assay (Lactuca sativa L) and real field-scale study of crop productivity (i.e., lettuce and tomato) were used. Although irrigation waters from the peri-urban area exhibited a higher frequency of detection and concentration of the assessed chemical contaminants than those of the pristine site (P1), no significant differences were found in seed phytotoxicity or crop productivity. In fact, the crops impacted by TWW showed higher productivity than the other farm plots studied, which was associated with the higher nutrient availability for plants.

Effects of potash mining on river ecosystems: An experimental study

In spite of being a widespread activity causing the salinization of rivers worldwide, the impact of potash mining on river ecosystems is poorly understood. Here we used a mesocosm approach to test the effects of a salt effluent coming from a potash mine on algal and aquatic invertebrate communities at different concentrations and release modes (i.e. press versus pulse releases). Algal biomass was higher in salt treatments than in control (i.e. river water), with an increase in salt-tolerant diatom species. Salt addition had an effect on invertebrate community composition that was mainly related with changes in the abundance of certain taxa. Short (i.e. 48 h long) salt pulses had no significant effect on the algal and invertebrate communities. The biotic indices showed a weak response to treatment, with only the treatment with the highest salt concentration causing a consistent (i.e. according to all indices) reduction in the ecological quality of the streams and only by the end of the study. Overall, the treatment's effects were time-dependent, being more clear by the end of the study. Our results suggest that potash mining has the potential to significantly alter biological communities of surrounding rivers and streams, and that specific biotic indices to detect salt pollution should be developed.

Chloride and sulphate toxicity to Hydropsyche exocellata (Trichoptera, Hydropsychidae): Exploring intraspecific variation and sub-lethal endpoints

The rivers and streams of the world are becoming saltier due to human activities. In spite of the potential damage that salt pollution can cause on freshwater ecosystems, this is an issue that is currently poorly managed. Here we explored intraspecific differences in the sensitivity of freshwater fauna to two major ions (Cl(-) and SO4(2-)) using the net-spinning caddisfly Hydropsyche exocellata Dufour 1841 (Trichoptera, Hydropsychidae) as a model organism. We exposed H. exocellata to saline solutions (reaching a conductivity of 2.5mScm(-1)) with Cl(-):SO4(2-) ratios similar to those occurring in effluents coming from the meat, mining and paper industries, which release dissolved salts to rivers and streams in Spain. We used two different populations, coming from low and high conductivity streams. To assess toxicity, we measured sub-lethal endpoints: locomotion, symmetry of the food-capturing nets and oxidative stress biomarkers. According to biomarkers and net building, the population historically exposed to lower conductivities (B10) showed higher levels of stress than the population historically exposed to higher conductivities (L102). However, the differences between populations were not strong. For example, net symmetry was lower in the B10 than in the L102 only 48h after treatment was applied, and biomarkers showed a variety of responses, with no discernable pattern. Also, treatment effects were rather weak, i.e. only some endpoints, and in most cases only in the B10 population, showed a significant response to treatment. The lack of consistent differences between populations and treatments could be related to the high salt tolerance of H. exocellata, since both populations were collected from streams with relatively high conductivities. The sub-lethal effects tested in this study can offer an interesting and promising tool to monitor freshwater salinization by combining physiological and behavioural bioindicators.

Sulphur and oxygen isotope analysis to identify sources of sulphur in gypsum-rich black crusts developed on granites

We describe the results of sulphur and oxygen isotope analyses used to identify sources of the gypsum present in black crusts that grow on the granite of historical buildings. The crusts were sampled at various locations in and near the city of Vigo (NW Spain) and were analysed for their sulphur content and δ(34)S and δ(18)O isotope ratios. Sampled crusts had δ(34)S values of 7.3‰ to 12.9‰ and δ(18)O values of 6.56‰ to 12.51‰. Sampled as potential sulphur sources were bulk depositions, seawater, foundation, ashlar and construction materials and combustion residues. The results indicated marine and, to a lesser extent, anthropogenic, origins for the sulphur and ruled out the contribution of sub-soil sulphates by capillary rise from building foundations. Isotope analyses would indicate that cement and mortar were enriched in sulphur after their application in buildings. The fact that facade orientation (towards the sea or fossil fuel pollution sources) was correlated with sulphur isotope distribution pointed to various contributions to black crust formation.

Changing ecosystem service values following technological change

Research on ecosystem services has focused mostly on natural areas or remote places, with less attention given to urban ecosystem services and their relationship with technological change. However, recent work by urban ecologists and urban designers has more closely examined and appreciated the opportunities associated with integrating natural and built infrastructures. Nevertheless, a perception remains in the literature on ecosystem services that technology may easily and irreversibly substitute for services previously obtained from ecosystems, especially when the superiority of the engineered system motivated replacement in the first place. We emphasize that the expected tradeoff between natural and manufactured capital is false. Rather, as argued in other contexts, the adoption of new technologies is complementary to ecosystem management. The complementarity of ecosystem services and technology is illustrated with a case study in Barcelona, Spain where the installation of sophisticated water treatment technology increased the value of the ecosystem services found there. Interestingly, the complementarity between natural and built infrastructures may remain even for the very ecosystems that are affected by the technological change. This finding suggests that we can expect the value of ecosystem services to co-evolve with new technologies. Technological innovation can generate new opportunities to harness value from ecosystems, and the engineered structures found in cities may generate more reliance on ecosystem processes, not less.

The combined effect of abandoned mines and agriculture on groundwater chemistry

Although it is well known that both mining and agriculture disturb groundwater quality, their mutual interactions are much less well documented, though agricultural activities may prevail once mining operations have ended. To study these potential interactions and their impacts on water chemistry, we monitored the chemical composition of groundwater at the outlet of a gold exploration gallery in an area of intensive agricultural activity along with an isotopic study of the groundwater, a reactive artificial tracer test that involved injecting H2O2 into the gallery, and geochemical modelling. The isotopic study revealed denitrification of the NO3-bearing groundwater that takes place through oxidation of the sulphide minerals associated with the gold deposit and leads to anomalous concentrations of some metals such as Zn, Co and Ni. It also contributes to liberating As into the groundwater, where the tracer test confirmed that As is sensitive to the redox conditions. The currently observed high arsenic concentrations in the groundwater are interpreted as resulting mainly from the former mining activities through a remobilization of As sorbed on or co-precipitated with the iron oxides that formed when the gallery was excavated. The geochemical modelling enabled us to calculate the respective role of each process involved in the As accumulation in the groundwater. It is also inferred that NO3 contamination from agricultural activities disturbs arsenic remobilization--by consuming available electron donors (e.g. organic matter), NO3 limits the reduction of iron oxides and consequently the release of arsenic.

Relative vs. absolute statistical analysis of compositions: a comparative study of surface waters of a Mediterranean river

Most hydrogeological research includes some sort of statistical study, which is generally conducted on the raw measures of chemical variables, though there are several theoretical and practical studies warning against this practice. Arguments refer mainly to the positive character of this type of data, and to the fact that they carry only information about the relative abundance of each component on the whole, what makes techniques based on correlation, like the widely used Principal Component Analysis (PCA), loose their meaning. The solution proposed by Aitchison (1982, Journal of the Royal Statistical Society, Series B 44(2), 139-177)-based on working with log-ratios of observations-is equivalent to define a new distance between compositions and to adapt usual statistical techniques to it. To illustrate its effect, our study compares the performance of the biplot-a PCA graphical technique-according to the usual Euclidean and to the Aitchison distance. The study is conducted on a set of 14 molarities measured monthly through the years 1997-1999 at 30 different stations along the Llobregat River and its tributaries (Barcelona, NE Spain). Ordinary analysis, implicitly based on an Euclidean distance, presents some deficiencies, mainly because it only captures major ion variations and the inferred relationship between them actually depends on other non-relevant variables, such as water mass. An analysis based on compositional distances captures variations of all the ions; it is robust against the inclusion of non-relevant variables in the analysis; and it offers a way to build factors expressed as equilibrium equations. In our case, two promising factors are extracted, showing the different anthropogenic and geological pollution sources of the rivers.

Fertilizer characterization: isotopic data (N, S, O, C, and Sr)

A detailed isotopic characterization (delta15N(Ntotal), delta15N(NO3), delta18O(NO3), delta34S(SO4), delta18O(SO4), (delta13C(Ctotal), and 87Sr/86Sr) of 27 commercial fertilizers used in Spain is presented in this paper. Results together with a compilation of fertilizer isotopic published data are used for two purposes: (i) to identify the origin of the primary constituents and raw materials used in fertilizer manufacture and relate these data with their heavy metals and rare earth elements (REE) contents; (ii) to compare the fertilizer isotopic signatures with natural values and other anthropogenic pollutants and evaluate the usefulness of multi-isotopic analyses to trace fertilizer contaminations in future study cases. Isotope data permit us to know, in most cases, the origin of the primary constituents of fertilizers, and the 87Sr/86Sr ratio distinguishes the origin of the phosphate content--phosphorites or carbonatites--which in turn implies a qualitatively defined and potentially contaminant presence of REE and heavy metals in fertilizers. Delta15N, delta34S, and 87Sr/86Sr have already been used to trace fertilizer contaminations. Their utility can be improved by the coupled use of delta15N(NO3)-delta18O(NO3) and delta34S(SO4)-delta18O(SO4) to evaluate the fractionation processes that can affect contaminants. Moreover, multi-isotopic analyses, using heavy isotopes, allow us to see beyond the fractionation effects to the fertilizer stable isotope signatures and a better distinction from other anthropogenic contaminants.