Fluxes of trichloroacetic acid through a conifer forest canopy

Controlled-dosing experiments with conifer seedlings have demonstrated an aboveground route of uptake for trichloroacetic acid (TCA) from aqueous solution into the canopy, in addition to uptake from the soil. The aim of this work was to investigate the loss of TCA to the canopy in a mature conifer forest exposed only to environmental concentrations of TCA by analysing above- and below-canopy fluxes of TCA and within-canopy instantaneous reservoir of TCA. Concentrations and fluxes of TCA were quantified for one year in dry deposition, rainwater, cloudwater, throughfall, stemflow and litterfall in a 37-year-old Sitka spruce and larch plantation in SW Scotland. Above-canopy TCA deposition was dominated by rainfall (86%), compared with cloudwater (13%) and dry deposition (1%). On average only 66% of the TCA deposition passed through the canopy in throughfall and stemflow (95% and 5%, respectively), compared with 47% of the wet precipitation depth. Consequently, throughfall concentration of TCA was, on average, 1.4 × rainwater concentration. There was no significant difference in below-canopy fluxes between Sitka spruce and larch, or at a forest-edge site. Annual TCA deposited from the canopy in litterfall was only 1–2% of above-canopy deposition. On average, 800 μg m−2 of deposited TCA was lost to the canopy per year, compared with estimates of above-ground TCA storage of 400 and 300 μg m−2 for Sitka spruce and larch, respectively. Taking into account likely uncertainties in these values (±50%), these data yield an estimate for the half-life of within-canopy elimination of TCA in the range 50–200 days, assuming steady-state conditions and that all TCA lost to the canopy is transferred into the canopy material, rather than degraded externally. The observations provide strong indication that an above-ground route is important for uptake of TCA specifically of atmospheric origin into mature forest canopies, as has been shown for seedlings (in addition to uptake from soil via transpiration), and that annualized within-canopy elimination is similar to that in controlled-dosing experiments

The production and degradation of trichloroacetic acid in soil: results from in situ soil column experiments

Previous work has indicated that the soil is important to understanding biogeochemical fluxes of trichloroacetic acid (TCA) in the rural environment, in forests in particular. Here, the hydrological and TCA fluxes through 22 in situ soil columns in a forest and moorland-covered catchment and an agricultural grassland field in Scotland were monitored every two weeks for several months either as controls or in TCA manipulation (artificial dosing) experiments. This was supplemented by laboratory experiments with radioactively-labelled TCA and with irradiated (sterilised) soil columns. Control in situ forest soil columns showed evidence of net export (i.e. in situ production) of TCA, consistent with a net soil TCA production inferred from forest-scale mass balance estimations. At the same time, there was also clear evidence of substantial in situ degradation within the soil (~70% on average) of applied TCA. The laboratory experiments showed that both the formation and degradation processes operate on time scales of up to a few days and appeared related more with biological rather than abiotic processes. Soil TCA activity was greater in more organic-rich soils, particularly within forests, and there was strong correlation between TCA and soil biomass carbon content. Overall it appears that TCA soil processes exemplify the substantial natural biogeochemical cycling of chlorine within soils, independent of any anthropogenic chlorine flux

Laboratory dissolution studies of rocks from the Borrowdale volcanic group (English Lake District).

Laboratory studies were conducted to investigate the rates ofrelease of Na, Mg, Al, Si, K, Ca and Fe from 10 samples of metamorphosed igneous rock of the Borrowdale Volcanic Group (BVG), consisting mainly of plagioclase feldspars, chlorite andquartz, with minor amounts of hornblende, epidote and carbonates.Experiments were performed using freshly-prepared rock pieces (ca. 12 mm cubes), in batch mode, but with frequent changes of the solution phase so that accumulation of dissolved solutes wasminimised. The initial element release rates were relatively high, but declined with time to reach approximate (pseudo-) steady state conditions. Element release rates declined withpH in the pH range 2–7, the dependence upon pH decreasing in the order Al Fe > Si > Mg Ca > K Na. Thepseudo-steady state rates for Si were comparable to steady state values for single minerals. Calcium showed the greatestsample-to-sample variation (more than 100-fold). Rock dissolutionwas far from stoichiometric, with Ca and Mg being present in thesolution phase in proportions greater than in the rock, and Al and Si in lower proportions. In some samples the release rates ofMg and Ca were equal, while in others the Ca rate was up to 100times that of Mg. The rate of release of Ca is correlated with the carbonate content of the rocks. The results indicate that the main source of Ca in the faster-dissolving samples is calcite, while the highest release rates of Mg are consistent with dissolution of dolomite. Aluminium, Si and Fe are probablyreleased predominantly from chlorite. The results are discussed in terms of the supply of base cations to stream waters drainingcatchments underlain by rocks of the BVG

The association of weather and bathing water quality on the incidence of gastrointestinal illness in the west of Scotland

The associations with weather and bathing water quality on infectious intestinal disease (IID) were investigated using data from two Scottish NHS Board areas. Monthly counts of viral and non-viral gastrointestinal infections were modelled as a smooth function of temperature, relative humidity and average monthly counts of faecal indicator organisms, respectively, adjusting for season and long-term trend effects. Strong seasonal patterns were observed for each group of pathogens. Peak viral gastrointestinal infection was in May while that of non-viral gastrointestinal infections was in July. A statistically significant negative association existed between weather (temperature and humidity) and viral infection. Average levels of non-viral gastrointestinal infections increased as temperature and relative humidity increased. Increasing levels of faecal indicator organisms in bathing waters were also associated with an increase in the average number of viral and non-viral gastrointestinal infections at the ecological level. Future climate change and prolonged precipitation events may result in increasing levels of faecal indicator organisms in bathing waters leading to likely increases in IIDs

Extreme value theory applied to the definition of bathing water quality discounting limits

The European Community Bathing Water Directive (European Parliament, 2006) set compliance standards for bathing waters across Europe, with minimum standards for microbiological indicators to be attained at all locations by 2015. The Directive allows up to 15% of samples affected by short-term pollution episodes to be disregarded from the figures used to classify bathing waters, provided certain management criteria have been met, including informing the public of short-term water pollution episodes. Therefore, a scientifically justifiable discounting limit is required which could be used as a management tool to determine the samples that should be removed. This paper investigates different methods of obtaining discounting limits, focusing in particular on extreme value methodology applied to data from Scottish bathing waters. Return level based limits derived from threshold models applied at a site-specific level improved the percentage of sites which met at least the minimum required standard. This approach provides a method of obtaining limits which identify the samples that should be removed from compliance calculations, although care has to be taken in terms of the quantity of data which is removed. (c) 2009 Elsevier Ltd. All rights reserve

Addressing analytical uncertainties in the determination of trichloroacetic acid in soil

Soil is an important compartment in the environmental cycling of trichloroacetic acid (TCA), but soil TCA concentration is a methodologically defined quantity; analytical methods either quantify TCA in an aqueous extract of the soil, or thermally decarboxylate TCA to chloroform in the whole soil sample. The former may underestimate the total soil TCA, whereas the latter may overestimate TCA if other soil components (e.g. humic material) liberate chloroform under the decarboxylation conditions. The aim of this work was to show that extraction and decarboxylation methods yield different TCA concentrations because the decarboxylation method can also determine bound TCA. Experiments with commercial humic acid solutions showed there was no additional chloroform formation under decarboxylation conditions, and that all TCA in a TCA–humic acid mixture could be quantitatively determined (108 ± 13%). Anion exchange resin was used as a provider of solid-phase TCA binding; only 5 ± 1% of a TCA solution mixed with the resin was present in the aqueous extract subsequently separated from the resin, yet the decarboxylation method yielded mass balance (123 ± 22%) with TCA remaining in the resin. In aqueous extraction of a range of soil samples (with or without added TCA spike), the decarboxylation method was able to satisfactorily account for TCA in the extractant + residue post-extraction, compared with whole-soil TCA (+ spike) pre-extraction: e.g. mass balances for unspiked soil from Sikta spruce and larch forest were 99 ± 8% and 93 ± 6%, respectively, and for TCA-spiked forest and agricultural soils were 114 ± 13% and 102 ± 2%. In each case recovery of TCA in the extractant was substantially less than 100% (<20% for unspiked soils, <55% for spiked soils). Extraction efficiencies were generally lower in more organic soils. The results suggest that analytical methods which utilise aqueous extraction may underestimate whole-soil TCA concentrations. Application of both methodologies together may enhance insight into TCA behaviour in soil