A critical evaluation of the use of the moss technique to monitor air pollution

Passive biomonitoring with terrestrial mosses, i.e. the “moss biomonitoring technique”, constitutes a useful tool for the study of the atmospheric deposition of heavy metals. However, it has limitations, some of which have been deeply assessed in this doctoral thesis. Thus, the temporal variability of the concentrations of several nutrients and pollutants in Pseudoscleropodium purum and the effect of growth on the concentrations of elements in segments of different ages of P. purum have been assessed (Chapters I and II respectively). Besides, the possible development of differences in the accumulation capacities of mosses that have grown in environments under different levels of pollution (Chapter III), and the relationship between the concentrations of several heavy metals in mosses and in bulk deposition (Chapters IV, V and VI), have also been discussed. Finally, despite the limitations found in the first part of this thesis (Chapters I to VI), it has been demonstrated that the technique enables researchers to distinguish between contaminated and uncontaminated sites, to identify small scale pollution sources, and to map spatial and temporal patterns of the atmospheric heavy metal deposition However, its application in environmental policy making is still limited due to the lack of a reliable, scientifically rigorous and homogenized protocol for the technique. Therefore a critical review of the available literature on passive biomonitoring with terrestrial mosses has been made (Chapter VII) in order to propose a protocol, as harmonised as possible, based on the results of the methodological studies published to date. Therefore, it can be concluded in the basis of all the results presented in this thesis, together with previously reported findings, that passive biomonitoring studies with terrestrial mosses provide qualitative and/or semi-quantitative rather than quantitative information. Interpretation of the results of this type of study must therefore be reconsidered; however, this does not mean that the information obtained is not useful. Such reconsideration, together with true harmonization of the technique (by publication of a protocol exclusively based on scientific criteria), should bridge the gap between the scientific application of the technique and its application in environmental policy making

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 conclusionsAuthors belong to the Grupo de Referencia Competitiva GRC GI-1252/GPC2020–23 (ED431C 2020/19) which is co-funded by Xunta de Galicia and ERDF (EU)S

Mythbusters: unravelling the pollutant uptake processes in mosses for air quality biomonitoring

Terrestrial mosses have been used for more than 50 years to monitor air pollution. We argue, however, that their value as biomonitors is based on two widespread but partially erroneous assumptions concerning their morphological structure (the structural myth) and physicochemical characteristics (the physicochemical myth). The structural myth consists of the oversimplification of the moss morphological structure. The physicochemical myth recognizes their high cation exchange capacity (CEC) as the only pathway for pollutant uptake. Here, we gather and discuss the evidence demonstrating that these assumptions are misleading and focus the discussion on the aspects that make mosses good biomonitors of air pollution. First, we show that these plants (i) do have a cuticle, whose structure and composition differs among species, (ii) can have epidermal cells, that differ in shape and thickness from other cell types, (iii) have a vascular system, whose degree of development is lineage- and species-specific, and (iv) have rhizoids, that can absorb water, nutrients and pollutants. The effect of these traits in the pollutant uptake processes has been understudied in biomonitoring studies. Second, we show that mosses (i) do not concentrate as much pollutants as they could according to their high CEC, (ii) can retain large amounts of particles containing atmospheric pollutants in their surfaces, and (iii) in many contexts, the spatial structure of the concentrations of pollutants in mosses depicts the pattern expected for atmospherically deposited particles. Thus, the quality of these organisms as biomonitors of air pollution also lies in their high capacity to retain particles. We do call for more research on how moss structural and physiological traits affect pollutant uptake dynamics and recommend researchers using mosses as air quality biomonitors to face critically to inaccurate or insufficiently demonstrated assumptions in this contextThe research of J. M-A and E. N-O has been supported by the grant PGC2018-093824-B-C42 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”S

Analysis of intra-thallus and temporal variability of trace elements and nitrogen in Fucus vesiculosus: Sampling protocol optimization for biomonitoring

To advance the methodological standardization of the biomonitoring technique using macroalgae, we comprehensively characterized the intra-thallus and temporal patterns of variation in concentrations of a wide set of elements (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Ni, Pb, Zn, N) and δ15N signal in 6 consecutive Fucus vesiculosus apical dichotomous sections collected monthly over a four-year period (2015–2019) at 3 sites on the NW coast of Spain. The concentrations of Al, Co, Fe, Ni, Pb and Zn increased significantly from the youngest to the oldest dichotomies regardless of the sampling time and collection site; As, Cd, N and δ15N showed the opposite trend. Time series analysis revealed a significant and consistent seasonal variation of As, Cd, Co, Cu, Fe, Hg, Ni, Zn, N and δ15N concentrations, with maximum values in winter and minimum values in summer. We discussed the possible mechanisms driving these two sources of variation, and proposed an efficient and effective sampling strategy to minimize their impact in the results of biomonitoring studies, in which the part of the algal thallus selected for chemical analysis and the sampling frequency were carefully considered. This protocol will improve the conclusions and comparability of biomonitoring data from coastal environments.En prens