Fine-tuning the use of moss transplants to map pollution by Potentially Toxic Elements (PTEs) in urban areas.

Mosspheres are a kind of moss transplants which offer a novel approach for detecting atmospheric pollution using devitalized mosses, as they reflect the atmospheric deposition of certain elements and polycyclic hydrocarbons. However, due to the unique features of the mosspheres such as the low elemental concentrations in the cultured material, the data treatment needs to be different from that of conventional biomonitoring studies. In this article, our objectives are to identify the best parameter for expressing the levels of chemical elements accumulated by mosspheres, and to apply a recently developed method to assess the probability of pollution of each sample and of the study area. To do this, we used data from a study in which 81 mosspheres were exposed in a medium-sized city in southwestern Europe. Comparing different pollution indices, we selected the enrichment rate (ER) as the most useful, as it is resilient to fluctuations in the initial concentrations and takes into account the time factor, allowing for greater comparability among studies. Then, we determined that the statistical distribution of the ERs of most elements fitted a normal distribution, showing that most samples did not differ significantly from the background concentrations for these elements. On the other hand, for Ni, Pb and Zn there was a subpopulation of samples above background values. In these cases, we determined the probability of pollution of each sample. Finally, we used indicator kriging to calculate the probability of pollution across the study area, identifying the polluted areas, which for some elements match the distribution of the main industries and highways, indicating that this is a suitable protocol to map elemental pollution in urban areas.

What dead seaweeds can tell us about metal uptake and their application to control marine pollution.

The mechanisms of trace element uptake by seaweeds are still unknown, despite being key to understand the impact of pollution in coastal environments. This knowledge gap, in addition to the lack of standardization, have also hindered the use of seaweeds to monitor seawater pollution. To address these shortcomings, we tested the use of devitalization as a pre-exposure treatment for brown seaweed transplants, and we compared devitalized and fresh transplants to gain some insights into the mechanisms of element uptake. We exposed four types of Fucus vesiculosus transplants in 6 sites for 4, 8 and 20 days: fresh and devitalized (dried or boiled) algal segments held in mesh bags, and whole algal thalli imitating natural conditions. We then determined he concentrations of 11 trace elements in the algal tissues. The element concentrations were highest in the devitalized transplants, but the material lost consistency and weight throughout the exposure period, limiting their use to short periods. We proposed several factors that may contribute to the different accumulation patterns between treatments, and examined the implications for the uptake mechanisms, revealing that two of the most important are surface adsorption of sediment particles and chemical bounds to extracellular components.

High Hg biomagnification in North Atlantic coast ecosystems and limits to the use of δ15N to estimate trophic magnification factors.

Mercury contamination is a global environmental problem. This pollutant is highly toxic and persistent which makes it extremely susceptible to biomagnify, i.e. increase its concentrations as it moves up the food chain, reaching levels that threaten wildlife and, ultimately, ecosystems' function and structure. Mercury monitoring is thus crucial to determine its potential to damage the environment. In this study, we assessed the temporal trends of the concentrations of Hg in two coastal animal species closely connected by a predator-prey interaction, and evaluated its potential transfer between trophic levels using the δ15N signatures of the two species. For this, we performed a multi-year survey of the concentrations of total Hg and the values of δ15N in the mussel Mytilus galloprovincialis (prey) and the dogwhelk Nucella lapillus (predator) sampled along ∼1500 km of the North Atlantic coast of Spain over a 30-year period (five surveys between 1990 and 2021). Concentrations of Hg decreased significantly between the first and the last survey in the two species studied. Except for the 1990 survey, the concentrations of Hg in mussels were amongst the lowest registered in the literature for the North East Atlantic Ocean (NEAO) and the Mediterranean Sea (MS) between 1985 and 2020. Nonetheless, we detected Hg biomagnification in almost all surveys. Worryingly, trophic magnification factors obtained here for total Hg were high and comparable to the found in the literature for methylmercury, the most toxic and readily biomagnified form of this element. The δ15N values were useful to detect Hg biomagnification under normal circumstances. However, we found that nitrogen pollution of coastal waters differentially affected the δ15N signatures of mussels and dogwhelks limiting the use of this parameter for this purpose. We conclude that Hg biomagnification could constitute an important environmental hazard even when found at very low concentrations in the lower trophic levels. Also, we warn that use of δ15N in biomagnification studies when there is some underlying nitrogen pollution problem might lead to misleading conclusions.

Polycyclic aromatic hydrocarbons (PAHs) levels in PM10 and bulk deposition using Mosspheres: A pilot study in an urban environment.

Study air polycyclic aromatic hydrocarbons (PAHs) capturing the spatial variability of their concentrations is not economically feasible with conventional methods. In the present work we tested, for the first time and under real conditions, the suitability for intensive monitoring and mapping these contaminants of innovative, cost-effective passive air samplers known as "Mosspheres". The Mosspheres, filled with a devitalised Sphagnum palustre L. moss clone, were placed in a 575 m. grid in a medium-sized European city for three months. Concentrations in the moss tissues of 15 priority PAHs, including benzo(a)pyrene, were determined and converted into PM10 and bulk deposition with the equations proposed in a recent study. Low concentrations of PAHs were detected, with only a few enriched points never exceeding the legal thresholds, near industrial areas and busy roads. Despite these low PAH concentrations, Mosspheres were able to detect spatial structure for several PAHs and high-resolution pollution maps were constructed for these compounds. The results prove the high sensitivity and suitability of Mosspheres for mapping PAH levels and for quantitative (i.e. PAHs with 4 or more rings) and qualitative (3-ring PAHs) monitoring. Thus, this study supports their widespread application and its potential inclusion in European Directives on air quality control.

Do we know the cellular location of heavy metals in seaweed? An up-to-date review of the techniques.

Seaweeds are dominant organisms in coastal environments. However, in the context of global change, the integrity of these organisms is threatened by metal pollution. It is therefore important to understand how seaweeds are affected by metal concentrations in the water. Measuring the concentrations of metals in seaweed provides information about the effects of metal pollution on the seaweeds themselves and their ecosystems. Nonetheless, correct interpretation of this type of analysis requires knowledge of the cellular location of the pollutants, as the effects will differ depending on whether the metals are present in particles adhered to the surface, attached to external polysaccharides or dissolved in the cytoplasm. Thus, the objectives of this study were to compile the available information on the subcellular distribution of metals in seaweeds and to conduct a critical review of the information. We found that the existing studies provide contrasting, sometimes contradictory, results. Thus, metals have been detected entirely intracellularly and also mainly outside of the cells. In all of the studies reviewed, which used different techniques (mainly extracellular elution, X-ray microanalysis and centrifugation), methodological and/or conceptual problems were identified that raise questions about the effectiveness of each approach. To obtain reliable information about the distribution of metals in algal cells, further studies must be conducted that take into consideration the differences between elements and algal species and the limits of the methods used to measure the elements.

Plant-air partition coefficients for thirteen urban conifer tree species: Estimating the best gas and particulate matter associated PAH removers.

Polycyclic Aromatic Hydrocarbons (PAHs) are an important class of pollutants which mostly come out from incomplete combustion of organic materials including fossil fuels. For this reason, they are often found at high concentrations in cities, contaminating air with their gas and particle phase. While European Union policies try to reduce their concentrations, huge efforts are still devoted to mitigate the pollution by PAHs. One such measure of mitigation is the use of plants in capturing PAHs and other chemicals due to the ability of leaves in filtering both gas and particle fractions. In this work thirteen conifer species among those frequently living in temperate and Mediterranean cities were selected and concentrations of 16 PAHs were measured in needles. The data for spruce were used to back-calculate air concentrations of PAHs which were later used to obtain specific equations of plant-air partition coefficient (KPA). The results showed that the difference in total PAH uptake between the most (Pinus pinaster) and the least (Picea abies) efficient tree was close to an order of magnitude. Looking to the capability of the different species in enriching the particulate matter (PM) associated fraction of PAHs on their needles, Pinus pinaster was instead the least important (3.4% of total PAHs), while Cupressus lusitanica was the most important (34% of total PAHs). The new KPA equations can be used to fine tune the PAH uptake of a specific amount of plant biomass on air concentration reduction.

Establishment of background pollution levels and spatial analysis of moss data on a regional scale.

The determination of background pollution levels is fundamental for the interpretation of the results obtained from environmental biomonitoring. In this paper we propose a new probabilistic method, based on a Gaussian mixture model, for determining the distribution of regional background levels of different pollutants. The distribution of the reference level is used to categorize the observations as "background" or "above-background" and spatial statistical techniques are then applied to determine the probability of the background level being exceeded. To exemplify its use, we applied the method to concentrations of five potentially toxic elements (Cd, Cu, Hg, Pb and Zn) measured in the moss Pseudoscleropodium purum. The proposed method was applied to data resulting from sampling at ca. 150 sampling stations in a regular grid (15 × 15 km) in Galicia (NW Spain). Sampling was carried out in June in 2000 and 2002, and in March and September in 2004, 2006, 2008 and 2014. The proposed method yielded consistent results for all of the different sampling surveys, and the pollution levels were found to be closely related to the sources of pollution identified in the study region. In short, although not an optimal solution, the proposed method seems to be suitable and realistic for the qualitative assessment of regional pollution.

Finding Biomarkers in Antioxidant Molecular Mechanisms for Ensuring Food Safety of Bivalves Threatened by Marine Pollution.

Aquaculture production as an important source of protein for our diet is sure to continue in the coming years. However, marine pollution will also likely give rise to serious problems for the food safety of molluscs. Seafood is widely recognized for its high nutritional value in our diet, leading to major health benefits. However, the threat of marine pollution including heavy metals, persistent organic pollutants and other emerging pollutants is of ever-growing importance and seafood safety may not be guaranteed. New approaches for the search of biomarkers would help us to monitor pollutants and move towards a more global point of view; protocols for the aquaculture industry would also be improved. Rapid and accurate detection of food safety problems in bivalves could be carried out easily by protein biomarkers. Hence, proteomic technologies could be considered as a useful tool for the discovery of protein biomarkers as a first step to improve the protocols of seafood safety. It has been demonstrated that marine pollutants are altering the bivalve proteome, affecting many biological processes and molecular functions. The main response mechanism of bivalves in a polluted marine environment is based on the antioxidant defense system against oxidative stress. All these proteomic data provided from the literature suggest that alterations in oxidative stress due to marine pollution are closely linked to robust and confident biomarkers for seafood safety.

Testing different methods of estimating edaphic inputs in moss biomonitoring.

Although soil is known to contribute to the concentrations of elements in moss, protocols for atmospheric biomonitoring with terrestrial moss do not include recommendations on how to address this factor. As a result, researchers indiscriminately use a wide range of detection/correction methods without considering whether the results are equivalent. In this study, three of these methods were compared: i) use of the enrichment factor (EF) index; ii) calculation of the ratios of different elements in soil and moss, and subtraction of the contribution of soil concentrations from the raw concentrations of elements in mosses (SCS); and iii) positive matrix factorization (PMF), a receptor modelling method for source apportioning based on multivariate analysis techniques. The aim of the comparison was to determine whether the methods produce equivalent results and, if not, which method is the most appropriate for use in moss biomonitoring surveys. The data used corresponded to 146 samples of Pseudoscleropodium purum collected from a regular sampling grid of 15 × 15 km in Galicia (NW Spain). Comparison of the methods revealed that, although they yield relatively similar results, the corresponding interpretations are not equivalent and none of the methods provides a reliable estimate of the soil contribution to the concentrations of elements in moss samples. Independently of the technique applied, use of Ti as a reference element is not recommended, because, at least in this study, it was present at unusually high levels in moss. Given the absence of a reliable correction method and the fact that most elements are present in fairly high amounts in the soil, we recommend using atmospheric biomonitoring with moss only for Cu, Zn and Cd, i.e. for those elements in moss for which the soil contributes very low amounts and corrections are not therefore necessary.

Temporal trends in mercury concentrations in raptor flight feathers stored in an environmental specimen bank in Galicia (NW Spain) between 2000 and 2013.

Temporal trends in Hg concentrations were investigated in primary flight feathers from 319 specimens of three birds of prey: P7 in the northern goshawk (Accipiter gentilis), P6 in the common buzzard (Buteo buteo) and P5 in the tawny owl (Strix aluco). The samples were stored in a regional environmental specimen bank and belonged to specimens which died between 2000 and 2013 in Galicia (NW Spain). We would expect to see a decline in Hg concentrations across the study period, as data of atmospheric emissions show a gradual reduction of this pollutant in Europe in the last two decades. The study did not reveal any temporal pattern in Hg concentrations of feathers in any of the three species for the study period, may be due to the persistence of Hg in the environment, but showed a low level of contamination by this metal in the study area. In addition, the results show high intra-specific, as well as, inter-annual and inter-specific variability in data, mainly attributed to the level of exposure of the raptors to this pollutant and to the biomagnification process of Hg through food chains. These findings indicate that the high variability can be a limiting factor in the use of raptors for biomonitoring temporal patterns of Hg, but nevertheless, the technique provides qualitative information about the amount of Hg that reach the top of the terrestrial food chains.

Evergreen or deciduous trees for capturing PAHs from ambient air? A case study.

Tree canopies play a key role in the cycling of polycyclic aromatic hydrocarbons (PAHs) in terrestrial ecosystems, as leaves can capture PAHs from the air. In this study, accumulation of PAHs was compared in an evergreen species, P. pinaster, and in a deciduous species, Q. robur, in relation to some physio-morphological characteristics. For this purpose, pine needles and oak leaves collected from different sites across Galicia (NW Spain) were analysed to determine PAH contents, specific leaf area, stomatal density and conductance. Leaves and needles contained similar total amounts of PAHs. The major contribution of particle-bound PAHs in oak (the concentrations of 4- and 5-ring PAHs were two times higher, and those of 6-ring PAHs five times higher in oak than in pine) may be related to the higher specific leaf area (13 and 4 cm2 g-1 dry mass in respectively oak and pine). However, the major contribution of vapor-phase PAHs in pines may be affected by the stomatal conductance (two times higher in pine than in oak). Moreover, an increase in the diameter at breast height of trees led to an increase in accumulation of PAHs, with pine capturing higher amounts of low and medium molecular weight PAHs. The study findings underline the potential role of trees in improving air quality, taking into account the canopy biomass and life cycle.

Genetic structuring of the moss Pseudoscleropodium purum sampled at different distances from a pollution source.

In this study, we used amplified fragment length polymorphism analysis to investigate the genetic structure of the terrestrial moss Pseudoscleropodium purum (Hedw.) M. Fleish. naturally exposed to different levels of atmospheric deposition of heavy metals. We also determined the heavy metal concentrations in samples of this moss to evaluate whether there was a relationship between atmospheric pollution and population genetic diversity. A low level of genetic diversity and a limited gene flow among populations were observed which is in accordance to the prevalence of asexual reproduction in this species. In addition, no significant correlation was found between metal content and gene diversity in P. purum, probably because of the common history of the sampled populations and/or to the lack of a drastic reduction of the size of the population; nonetheless, a clear genetic structure was evident in relation to the existing pollution gradient. Thus, based on the results of the principal coordinate analysis and Bayesian analysis of the genotypes, the mixed structure of the second most polluted population would suggest an ongoing differentiation of metal-tolerant genotypes in the most polluted sites of the sampling area.

Assessing the effects of heavy metal contamination on the proteome of the moss Pseudoscleropodium purum cross-transplanted between different areas.

Protein expression was assessed in samples of Pseudoscleropodium purum cross-transplanted between one unpolluted (UNP) and two polluted (POLL) sites. Firstly, the level of expression (LE) of 17 proteins differed between native mosses from both types of sites, but differences were only maintained throughout the experiment for 5 of them. The LE of these five proteins changed over time in mosses transplanted from UNP to POLL and vice versa, becoming similar to that in autotransplants. However, these changes occurred slower than changes in the heavy metal concentrations measured in the same samples, and therefore they were not related to atmospheric pollution. Although the proteins identified were associated with moss metabolism, the expected growth reduction in samples autotransplanted within POLL (as a result of the down-regulation of photosynthesis-related proteins), did not occur. This supports the hypothesis that mosses growing in polluted areas adapt to heavy metal pollution and are able to reduce/overcome their toxic effects (i.e., reduced growth). Nevertheless, further specific research must be carried out to identify the proteins involved in this type of response, as lack of information on the bryophyte genome precludes us from reaching further conclusions.

Assessing the tolerance of the terrestrial moss Pseudoscleropodium purum to high levels of atmospheric heavy metals: a reciprocal transplant study.

We measured the concentrations of Cd, Cu, Hg, Pb and Zn in samples of the terrestrial moss Pseudoscleropodium purum reciprocally transplanted between an unpolluted and two polluted sampling sites. At the beginning of the experiment, the concentrations of all these elements differed significantly between mosses from the unpolluted site and mosses from the polluted sites. In general, the concentrations of the heavy metals in mosses from both polluted sites transplanted to the unpolluted site decreased until they reached the same levels as in autotransplants at this site (after 480-840 days). However, the concentrations of all heavy metals in mosses transplanted from the unpolluted site to both polluted sites increased to higher levels than in the autotransplants (except for Cu, Hg and Pb at one of the sampling sites). These results led us to conclude that mosses that have been continuously exposed to high atmospheric deposition of heavy metals undergo an adaptive response (probably genotypic) to such conditions. We therefore recommend active rather than passive biomonitoring of air quality in industrial environments because atmospheric deposition could be underestimated, and also recommend further investigation into the mechanisms involved in this response.

Selection of flight feathers from Buteo buteo and Accipiter gentilis for use in biomonitoring heavy metal contamination.

The concentrations of Hg were determined in all primary flight feathers from 20 specimens of Buteo buteo and 49 specimens of Accipiter gentilis, which had died in various Wildlife Recovery Centres in Galicia (NW Spain) between 2001 and 2009. The aim of the study was to standardize the feather or feathers that should be analyzed in each species to enable inter-individual comparison of the levels of contamination, taking into consideration any variability in the concentrations of Hg caused by the birds' molting patterns. For both species the results show a high degree of both inter (e.g. an individual of A. gentilis showed 426 ng g(-1) of Hg as median and 568 ng g(-1) as median absolute deviation, MAD) and intra-individual variability (e.g. primary feather number seven - P7 - of all the A. gentilis individuals showed 537 ng g(-1) of Hg as median and 1129 ng g(-1) as MAD). Although molting did not have a clear effect on the concentrations of Hg in the flight feathers, it was possible to identify the most representative feather in each individual, taking into account the amount of metal excreted in each feather and the intra-individual variability. For B. buteo use of flight feather P6 is recommended for Hg biomonitoring studies; the amount of Hg excreted to this feather was 509 ng as median, which represents the 14% (from 10 to 20%) of the total Hg present in all the primary feathers. For A. gentilis the recommended feather is P7, which has a median of 86 ng of Hg (corresponding to 12%, and varying between 5 and 22%).

The analysis of pollutant profiles by means of compositional analysis. An application to PCDD/F data.

Compositional analysis consists of a group of techniques used to manipulate closed (=compositional) data, i.e. multivariate data summing to a fixed quantity (proportions, percentages). It is based on the analysis of the relations among variables and the use of logarithmic transformations. It has been claimed that this group of techniques should be used to analyse profiles of pollutant sources because profiles themselves are proportions. We show in this paper that, for the exploratory analysis of these data, a good strategy is to combine the analysis done with and without transformation because they give different and complementary insights on the structure of the data. We discuss in particular the study of processes such as the mixing of pollutants produced by different sources and the exponential decay of concentrations with distance to the source found in many studies. The clr transformation is also appropriate for the study of the variables having small proportions, which remain concealed by the abundant variables when analysed without transformation. We present simulations to illustrate these ideas and we also apply these techniques to two data sets of PCDD/F content in moss tissues.