J.R. Aboal

Use of native and transplanted mosses as complementary techniques for biomonitoring mercury around an industrial facility

Terrestrial mosses were used simultaneously in passive (native species, Scleropodium purum and Hypnum cupressiforme) and active (S. purum transplants in moss bags) biomonitoring techniques in a study that aimed to demonstrate the compatibility of the two methods by detailed investigation of the spatial distribution of mercury in the surroundings of a chlor-alkali plant. Native mosses were sampled and transplants exposed (for periods of 30 days) at two different times of the year in order to take into account different environmental conditions (precipitation, temperature, prevailing winds, etc.). The concentrations of Hg in the native mosses ranged between 0.04 and 11.78 microg g(-1) in February and 0.26 and 12.7 microg g(-1) in September; in the transplants the concentrations ranged between 0.39 and 1.9 microg g(-1) in June and 0.036 and 2.75 microg g(-1) in November. These values are all within the ranges reported in the literature. The total concentrations were transformed into either contamination factors (CF) (by taking into account the background levels of Hg in the native mosses) or enrichment factors (EF) (by taking into account the initial concentrations in the transplants). In both cases, there was a clear relationship with the distance from the source of emission, irrespective of the time of year. Within the range of distances for which data were available for natives and transplants, the CF and EF were highly correlated. This implies that transplants sited in the area immediately surrounding the plant, where the density of native mosses was very low, can be used to determine the degree of contamination in this area. The study also illustrated that the native moss appeared to adapt to the surrounding environment because at an equal distance (> 500 m) from the source of emission the value of the CF for native mosses fell to 1, but the EF for transplanted mosses remained still high (5.2).

Moss bag biomonitoring: a methodological review.

Although the moss bag technique has been used for active biomonitoring for the past 40years, there is still no standardized protocol that enables application of the technique as a tool to monitor air quality. The aim of this review paper is to evaluate the degree of standardization of each of the variables that must be considered in applying the technique (i.e. the variables associated with preparation of the moss and moss bags, exposure of the bags, and post-exposure treatment). For this purpose, 112 scientific papers that report the methods used in applying the moss bag technique were consulted. Finally, on the basis of the conclusions reached, we propose a protocol that will enable each of these variables to be investigated separately, with the final aim of developing a standardized methodology.

Nitrogen concentrations in mosses indicate the spatial distribution of atmospheric nitrogen deposition in Europe

In 2005/6, nearly 3000 moss samples from (semi-)natural location across 16 European countries were collected for nitrogen analysis. The lowest total nitrogen concentrations in mosses (<0.8%) were observed in northern Finland and northern UK. The highest concentrations (≥ 1.6%) were found in parts of Belgium, France, Germany, Slovakia, Slovenia and Bulgaria. The asymptotic relationship between the nitrogen concentrations in mosses and EMEP modelled nitrogen deposition (averaged per 50 km × 50 km grid) across Europe showed less scatter when there were at least five moss sampling sites per grid. Factors potentially contributing to the scatter are discussed. In Switzerland, a strong (r(2) = 0.91) linear relationship was found between the total nitrogen concentration in mosses and measured site-specific bulk nitrogen deposition rates. The total nitrogen concentrations in mosses complement deposition measurements, helping to identify areas in Europe at risk from high nitrogen deposition at a high spatial resolution.

Is it possible to estimate atmospheric deposition of heavy metals by analysis of terrestrial mosses

Here we present a critical review of diverse research studies involving estimation of atmospheric deposition of heavy metals from the concentrations of the contaminants in terrestrial moss. The findings can be summarized as follows: i) significant correlations between the concentrations of contaminants in moss and bulk deposition were observed in only 40.1% of the cases in which the relationship was studied and in only 14.1% of the cases, the coefficient of correlation was >0.7; ii) some method-related problems were identified (i.e. small sample sizes, elimination of some data from the regression analyses, large distances between the moss sampling sites and the bulk precipitation collectors, differences in times of exposure of the moss samples and collection times for the bulk precipitation), so that the results of the studies may not be completely valid, and iii) evidence was found in the relevant literature that moss does not actually integrate the atmospheric deposition received. We also discuss the reason why, in accordance with the published data, bulk deposition cannot be correctly estimated by determination of the final concentrations of contaminants in the organism, such as the existence of different sources of contamination, the physicochemical characteristics of the sources of deposition, physicochemical processes to which the organism is subjected and the biological processes that take place in the moss. Taking into account the above findings, it was concluded that, except for certain elements and specific cases (i.e. Pb and Cd), atmospheric deposition of elements cannot be accurately estimated from the concentrations of metals and metalloids in moss tissues. However, the analysis of moss does provide information about the presence of contaminants in the atmosphere, their spatial and temporal patterns of distribution and how they are taken up by live organisms. Use of mosses is therefore recommended as a complementary (rather than an alternative) technique in the conventional analysis of bulk deposition of contaminants.

Effects of thinning on throughfall in Canary Islands pine forest — the role of fog

Throughfall was monitored over a one-year period in a 48-year-old Pinus canariensis plantation on the northern side of the island of Tenerife, nine years after light thinning (mean 15% of basal area (BA)) or heavy thinning (mean 56% of BA). Three plots of each treatment (light thinning, heavy thinning, no thinning) were studied, using a randomized block design. Mean total throughfall over the year of study was about 2.0 times the incident rainfall in the control plots, about 2.2 times rainfall in the lightly thinned plots, and about 1.8 times incident rainfall in the heavily thinned plots. The high throughfall-to-rainfall ratios are as expected, given the importance of fog entrapment in these forests. The statistical analysis indicated that the observed differences in throughfall are attributable to the treatments, not to plot topography. Throughfall showed significant relationships with actual BA, surface roughness (as tree height variability) and leaf area index (LAI), all of which varied significantly among treatments (as expected). Our results are unexpected as heavy thinning led to a long-term decline, not increase, in throughfall. The explanation for this result is the importance of fog entrapment may mean that reducing LAI and surface roughness (height variability) has a negative effect on throughfall. The long period elapsed between thinning and throughfall estimation means that LAI of light thinning plots exceeded pre-thinning values, and then throughfall values.

Country-specific correlations across Europe between modelled atmospheric cadmium and lead deposition and concentrations in mosses

Previous analyses at the European scale have shown that cadmium and lead concentrations in mosses are primarily determined by the total deposition of these metals. Further analyses in the current study show that Spearman rank correlations between the concentration in mosses and the deposition modelled by the European Monitoring and Evaluation Programme (EMEP) are country and metal-specific. Significant positive correlations were found for about two thirds or more of the participating countries in 1990, 1995, 2000 and 2005 (except for Cd in 1990). Correlations were often not significant and sometimes negative in countries where mosses were only sampled in a relatively small number of EMEP grids. Correlations frequently improved when only data for EMEP grids with at least three moss sampling sites per grid were included. It was concluded that spatial patterns and temporal trends agree reasonably well between lead and cadmium concentrations in mosses and modelled atmospheric deposition.

Sampling optimization at the sampling-site scale for monitoring atmospheric deposition using moss chemistry

Fifty samples of Scleropodium purum were collected from a single study area for individual analysis with the aim of optimizing the protocol for sampling terrestrial mosses in order to biomonitor atmospheric deposition. The concentrations of Ca, Cu, Fe, Hg, Ni, and Zn were determined in each sample and mass-weighted means were calculated. Analyses were also carried out on a composite sample. The distributions of the concentrations and the existence of spatial patterns were studied using semivariograms. The data for elements considered to be contaminants (Cu, Ni and Zn) were log-normally distributed and highly variable. Of the elements studied, only Ni and Zn were spatially dependent, due to atmospheric deposition. The three main sources of error introduced when making composite sample were determined, and possible means of reducing them were suggested. To summarize: (i) measurements were made on a composite sample—not on subsamples—leading to an error that was occasionally >20% (including analytical error) and that was basically unavoidable; (ii) differences in weight between the subsamples led to an error that was scarcely >2% and that could be easily reduced by using subsamples of similar weights; and (iii) sources of variation related to the number of subsamples in a composite sample may lead to an error >30% when the usual methodology is followed. We propose to collect a minimum of 30 subsamples wherever contamination is suspected.

Annual variability in heavy-metal bioconcentration in moss: sampling protocol optimization

The moss Scleropodium purum was sampled at four sampling stations, every 28 days over a period of three and a half years, and the tissue contents of Al, K, Ca, Mg, Cu, Mn, Fe, Na, Hg and Zn were determined in each of the samples. Autocorrelograms were used to study possible seasonal patterns of accumulation. A cyclic pattern of accumulation, repeated every 12 months, was revealed for Cu, K, Mg and Na, with maximum levels in winter and minimum levels in summer. The seasonal pattern of accumulation may be explained by the effect produced by desiccation of the moss during the summer months. To find the sampling design that best represents the intra-annual variability in the tissue contents of heavy metals, we proposed a series of sampling designs that combined different numbers of samplings and lag between samplings. These were then applied to the temporal series obtained and the one that best reflected the annual bioconcentration at a sampling station was selected. The proposed sampling design, recommended for application in future studies of atmospheric biomonitoring with terrestrial mosses, consists of two samplings separated by 6–7 months.

Sampling optimization, at site scale, in contamination monitoring with moss, pine and oak

With the aim of optimizing protocols for sampling moss, pine and oak for biomonitoring of atmospheric contamination and also for inclusion in an Environmental Specimen Bank, 50 sampling units of each species were collected from the study area for individual analysis. Levels of Ca, Cu, Fe, Hg, Ni, and Zn in the plants were determined and the distributions of the concentrations studied. In moss samples, the concentrations of Cu, Ni and Zn, considered to be trace pollutants in this species, showed highly variable long-normal distributions; in pine and oak samples only Ni concentrations were log-normally distributed. In addition to analytical error, the two main source of error found to be associated with making a collective sample were: (1) not carrying out measurements on individual sampling units; and (2) the number of sampling units collected and the corresponding sources of variation (microspatial, age and interindividual). We recommend that a minimum of 30 sampling units are collected when contamination is suspected.

Study of the air quality in industrial areas of Santa Cruz de Tenerife (Spain) by active biomonitoring with Pseudoscleropodium purum

A biomonitoring technique with terrestrial moss transplants (50 sampling sites in a regular grid) was used in an area of the city of Santa Cruz de Tenerife, close to an oil refinery and to an area of dense road traffic for a period of 2 months. The concentration of metals and metalloids (As, Cd, Hg, Ni, Pb and V) and 16 polycyclic aromatic hydrocarbons (PAHs) were determined. The density distribution was represented, the enrichment factors calculated and multifactorial analysis applied. In addition, contamination maps were elaborated on the basis of the bioconcentration obtained, and after confirming the existence of spatial structure, the response surfaces were represented. The results showed very high levels of contamination by Ni and V in the study area, with similar dispersal patterns observed for both. The concentrations of Cd, Hg, Pb and PAHs were lower. Active biomonitoring with terrestrial mosses was found to be a suitable technique for implementing inexpensive environmental monitoring programmes in urban and industrialized areas.