A method for studying the influence of Mn oxyhydroxides on the trace element content of aquatic bryophytes.

The main objective of this study was to develop and test a method of separating externally deposited Mn oxyhydroxides and co-precipitated elements from samples of aquatic moss (the moss Fontinalis antipyretica). The method, which uses 0.1 M hydroxylamine to dissolve the oxyhydroxides, was tested with samples collected in rivers with slightly acidic, well­oxygenated waters, where high rates of Mn precipitation occur. The method was effective (it extracted up to 84 % of the Mn) and selective (Fe oxyhydroxides were not extracted). The elements Ba, Cd, Zn and Ni were associated with the Mn oxyhydroxides, while Al, As, Cr, Cu, Fe, Hg and Pb were not. Deposition of Mn therefore increased the concentration of some elements in the moss samples. However, as Mn precipitation depends on Eh and pH, which are independent of the concentrations of the elements in water, the relationship between water and moss element concentrations is not clear (i.e. the data are noisy). This is a problem in biomonitoring studies, which assume a close relationship between element concentrations in moss and water. The value of the proposed extraction method is that it can be used to correct the effect of Mn deposition. We present an example of this correction applied to the Cd concentrations in the test data. We found that the noise introduced by the Mn, including age-related effects (observed by comparing concentrations in 0-2.5 and 2.2-5.0 cm sections from the shoot apex), can be reduced. Additionally, the correction revealed recent increases in Cd concentrations in one site that were not observed in the uncorrected data. Another finding of interest was the low content of total Mn and different extractability (of most elements) observed in moss samples collected in alkaline waters. Finally, we discuss how future studies designed for different environmental scenarios can benefit from application of the proposed method.

Influence of the storage procedure on the trace element content measured in the aquatic moss Fontinalis antipyretica Hedw.

Aquatic bryophytes have been used as pollution biomonitors for decades. Despite this, sample collection and preparation methods have not been standardized, which makes it difficult to compare the results of different studies. Most times, the samples have to be stored before processing, for example, when many of them are collected in a short time, as occurs in extensive pollution studies. Storage must be done in a way that does not change the pollutant concentrations in the samples. We studied whether the concentrations of Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn in the aquatic moss Fontinalis antipyretica were affected by three storage procedures: dry at room temperature, fresh (in refrigerator at 6°C), and frozen at -20°C. In addition, we evaluated whether the subsequent washing of the samples affected the concentrations of these elements differently depending on the storage method. Our results showed that the three methods were, in general, adequate since the concentrations did not change, and we did not observe differences between washed and unwashed samples either. Since the simplest method is refrigeration, we concluded that this is the best of them. However, the concentrations of Hg increased steadily over time in the fresh material, probably because of redistribution after volatilization from the basal parts of the mosses. We believe that the respiration of the plants lowered the concentrations of oxygen inside the hermetically sealed bags containing the samples, thus promoting the reduction of the Hg and its posterior volatilization and redistribution. We did not observe interactions between the storage method and the posterior washing of the samples. PRACTITIONER POINTS: We studied the influence of storage procedure on element content in aquatic mosses. The procedures were as follows: dried at room temperature, stored in refrigerator, and frozen. The procedures did not change the element contents, except for Hg in refrigerator. All the procedures seemed suitable, but refrigeration was the simplest one.

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.

The cotton-strip assay as an environmental surveillance tool for ecological integrity assessment of rivers affected by WWTP effluents.

Environmental impact studies of rivers affected by wastewater treatment plant (WWTP) effluents have been greatly restricted by the difficulties associated with carrying out bioassays in the field and also by the complex interactions between the pollutants contained in the discharges. The cotton-strip assay (CSA) enables study of the organic matter decomposition potential, an important ecosystem process in rivers, by taking all of the factors affecting this process into account. However, the CSA has never been used for assessment of WWTP effluents. In the present study, we selected six fluvial zones affected by discharges from small WWTPs and placed cotton strips at increasing distances from the discharge points in each zone. After 17 days, we evaluated decay of the strips by measuring cotton tensile strength loss (CTSL) and cotton mass loss (CML). We then determined the relationships between these parameters and various physico-chemical and biological properties in the water, as well as the δ15N isotopic signal and metal contents of aquatic mosses transplanted in the same sampling sites and used as biomonitors. Although the WWTPs were similar, some of the discharges stimulated and others inhibited decomposition of the cotton strips. This was probably due to differences in the proportions of various types of pollutants (with trophic or toxic effects) in the discharges. The CSA proved to be a simple, practical and economic bioassay and suitable for evaluating the ecological integrity of fluvial ecosystems.

Assessing changes in the toxicity of effluents from intensive marine fish farms over time by using a battery of bioassays.

Although intensive marine fish farming is often assumed to be eco-friendly, the associated activity can lead to chronic exposure of marine organisms to potentially toxic discharges. Moreover, despite the increasing popularity of integrated multi-trophic aquaculture (IMTA), studies of the effects of fish farm effluents are almost non-existent. In the present study, the changes in the toxic potential of effluents from five land-based marine fish farms in NW Spain subjected for different lengths of time to a biodegradation procedure (for 0, 48, 120, and 240 h) were assessed in a battery of bioassays including organisms from different trophic levels (Vibrio fischeri, Isochrysis galbana, and Paracentrotus lividus). The results of the bioassays at the different times were then considered together with farm water flow in the Potential Ecotoxic Effects Probe (PEEP) index. Despite the high volumes of effluents discharged, the generally low toxicity of the effluents hinders assessment of potentially toxic effects. However, dose-response curves and statistical analysis demonstrated the existence of toxic effects during the first five days of the biodegradation procedure, especially immediately after sampling. The proposed modification of the PEEP index better reflects the changes in toxicity over time. Graphical abstract ᅟ.

Differences in Metal Accumulation in the Growing Shoot Tips and Remaining Shoot Tissue in Three Species of Brown Seaweeds.

In this study we compared the accumulation of eight metals and two metalloids in the growing tips and the remaining shoot tissue of three species of brown seaweeds commonly used in biomonitoring studies (Fucus ceranoides, Fucus spiralis and Ascophyllum nodosum). Regression analysis of the data obtained showed that there was no statistically significant difference in accumulation in numerous cases; although most of the relationships were significant, many of the coefficients of determination were low. However, the concentrations of Mn and Zn in the growing tips were closely related to the concentrations in the rest of the tissue in all three species, possibly due to redistribution of these elements. Interspecies differences in bioconcentration of the elements may be partly explained by differences in the relative growth rates.

Contribution of atmospheric deposition to tissue concentrations of mercury in aquatic bryophytes.

In this biomonitoring study, we measured the temporal variations in concentrations of mercury in samples of aquatic bryophytes from rivers in a region that received large inputs of the metal via atmospheric deposition. In the first year of sampling, the presence of an important source of atmospheric deposition of Hg (a lignite-fired power plant) led, during the rainy season, to elevated concentrations of the metal in catchments situated downwind of the prevailing winds. High concentrations of the metal were even detected in samples from apparently clean rivers in isolated mountain sites within the downwind catchments. Substitution of the type of fuel (high quality imported carbon instead of brown coal) used in the power plant greatly reduced Hg emissions in subsequent years. Application of spatial interpolation techniques to dense monitoring networks with aquatic bryophytes, without taking into consideration the catchment borders, appears suitable for studying extensive atmospheric pollution derived from a large scale source of contamination. This study also demonstrates the importance of environmental specimen banks in retrospective studies of contamination, as they enable posterior analysis of contaminants that for various reasons cannot be analyzed at the time of sampling.

Arsenic and mercury in native aquatic bryophytes: differences among species.

This study investigated the capacities of five species of aquatic bryophytes to accumulate As and Hg from their natural habitats in rivers in Galicia (NW Spain). The distributions of the concentrations of both elements in all species were skewed to the right, with a higher incidence of extreme values in the As data, which may indicate a greater degree of contamination by this metalloid. There were no significant differences in the accumulation of either of the elements between the different species studied, which justifies their combined use as biomonitors of As and Hg, at least in the study area.

Design of an aquatic biomonitoring network for an environmental specimen bank.

The aim of the present study was to establish an aquatic biomonitoring network for the Galician Environmental Specimen Bank (BEAG) (NW Spain). For this, a sampling system was designed that comprised of 121 points distributed throughout Galician rivers, from which samples of water and of three species of bryophytes were collected. The results obtained allowed selection of 74 sampling points and 2 species (Fontinalis antipyretica Hedw. and F. squamosa Hedw.) as the most suitable for use in future BEAG sampling surveys. The two species selected showed a strong similarity in their capacity to accumulate the 17 elements determined (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, Se and Zn), as well as in their ecological preferences. Furthermore, the levels of contamination of epicontinental waters were lower than those observed in previous surveys.

Use of an environmental specimen bank for evaluating the impact of the Prestige oil spill on the levels of trace elements in two species of Fucus on the coast of Galicia (NW Spain).

In the present study we investigated possible contamination by trace elements due to the oil slick caused by the shipwreck of the Prestige oil tanker, in two species of brown macroalgae (Fucus vesiculosus and Fucus ceranoides) collected from the coastal area most severely affected by the spill (Galicia, NW Spain). The oil slick apparently did not cause significant increases in the concentrations of the trace elements studied, except vanadium. It appears that the magnitude of terrestrial inputs to coastal waters is sufficiently high to mask the inputs of trace elements from the fuel. The observed exception of V suggests that bioaccumulation of this element by the two species of Fucus may be used to indicate exposure to petrochemical products similar to the Prestige fuel. The findings of the study are another example of the importance of the existence of Environmental Specimen Banks for studies of this type.

Heavy metals in sandy sediments of the Rías Baixas (NW Spain).

We studied the concentrations of certain heavy metals in the total and labile fractions of sandy sediments from four embayments situated on the northwestern coast of Spain. In order to compensate for the effects of the heterogeneity in texture of the different samples, data were normalized. Organic carbon was the most suitable normalizing factor for copper, lead and zinc in the total fraction and copper in the labile fraction, and iron was the most suitable for the other metals in both fractions. Enrichment of copper, lead and zinc in these sediments may have been caused by sewage contamination. The percentages of extractability for chromiun were remarkable.