Fluoride accumulation and toxicity in wild small mammals

Populations of two species of small mammal, the field vole (Microtus agrestis L.) and the bank vole (Clethrionomys glareolus L.), inhabiting grasslands contaminated by industrial sources of fluoride were examined for fluoride concentrations in skeletal tissue and for morphological changes in the teeth. Concentrations of fluoride in teeth and bones were higher for C. glareolus than for M. agrestis at the chemical works and smelter sites. Severe dental lesions were recorded on the incisor and molar teeth of both species at the chemical works and smelter sites, with less marked damage at the mine tailings dam. This is attributed to inter-site differences in fluoride speciation and the consequent effects on the availability of fluoride in the diet for bioassimilation.     

Aquatic microcosm assessment of the effects of tylosin on Lemna gibba and Myriophyllum spicatum

Tylosin is a macrolide antibiotic commonly used for therapeutic treatment and prophylaxis in livestock. As part of a larger ecotoxicological study, the potential phytotoxic effects of tylosin on the rooted macrophyte Myriophyllum spicatum and the floating macrophyte Lemna gibba were assessed under semi-field conditions using 15 12 000-L microcosms. Concentrations of 0, 10, 30, 300 microg/L (n = 3), and 600, 1000, and 3000 microg/L (n = 1) were evaluated as part of separate ANOVA and regression analyses over an exposure period of 35 days. Fate of tylosin was monitored over time in the highest three treatments, where dissipation followed pseudo-first order kinetics with associated half-lives ranging from 9 to 10 days. For both M. spicatum and L. gibba, tylosin was found to cause no biologically significant changes to any endpoint assessed compared to controls at a Type I error rate of 0.1. However, subsequent power analyses revealed that there was generally insufficient power to declare that there were no significant differences at a Type II error rate of 0.2. Conclusions concerning biologically significant impacts were therefore further assessed based on other statistical criteria including comparisons of percent differences between replicated treatments and controls, minimum significant and minimum detectable differences, and coefficients of variation. Based on these criteria, at an ecological effect size of >20% change, tylosin was concluded to elicit no biologically or ecologically significant toxicity to M. spicatum or L. gibba. A hazard quotient assessment indicated that tylosin poses little risk to either species of macrophyte, with an HQ value calculated to be nearly three orders of magnitude below 1 (0.002).     

Effects of forest management on soil carbon: results of some long-term resampling studies

The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomass and soil C were studied in four forested sites in the southeastern US (mixed deciduous forests at Oak Ridge, TN and Coweeta, NC; Pinus taeda at Clemson, SC: and P. eliottii at Bradford, FL). In general, harvesting had no lasting effects on soil C. However, intensive temporal sampling at the NC and SC sites revealed short-term changes in soil C during the first few years after harvesting, and large, long-term increases in soil C were noted at the TN site in all treatments. Thus, changes in soil C were found even though lasting effects of harvest treatment were not. There were substantial differences in growth and biomass C responses to harvest treatments among sites. At the TN site, there were no differences in biomass at 15 years after harvest. At the SC site, greater biomass was found in the SAW than in the WTH treatment 16 years after harvest, and this effect is attributed to be due to both the N left on site in foliar residues and to the enhancement of soil physical and chemical properties by residues. At the FL site, greater biomass was found in the CTH than in the WTH treatment 15 years after harvest, and this effect is attributed to be due to differences in understory competition. Biomass data were not reported for NC. The effects of harvest treatment on ecosystem C are expected to magnify over time at the SC and FL sites as live biomass increases, whereas the current differences in ecosystem C at the TN site (which are due to the presence of undecomposed residues) are expected to lessen with time.     

Effects of increased deposition of atmospheric nitrogen on an upland Calluna moor: N and P transformations

This study determined the effects of increased N deposition on rates of N and P transformations in an upland moor. The litter layer and the surface of the organic Oh horizon were taken from plots that had received long-term additions of ammonium nitrate at rates of 40, 80 and 120 kg N ha(-1) yr(-1). Net mineralisation processes were measured in both field and laboratory incubations. Soil phosphomonoesterase (PME) activity and rates of N(2)O release were measured in laboratory incubations and root-surface PME activity measured in laboratory microcosms using Calluna vulgaris bioassay seedlings. Net mineralisation rates were relatively slow, with net ammonification consistently stimulated by N addition. Net nitrification was marginally stimulated by N addition in the laboratory incubation. N additions also increased soil and root-surface (PME) activity and rates of N(2)O release. Linear correlations were found between litter C:N ratio and all the above processes except net nitrification in field incubations. When compared with data from a survey of European forest sites, values of litter C:N ratio were greater than a threshold below which substantial, N input-related increases in net nitrification rates occurred. The maintenance of high C:N ratios with negligible rates of net nitrification was associated with the common presence of ericaceous litter and a mor humus layer in both this moorland as well as the forest sites.     

Aldehyde and monocyclic aromatic hydrocarbon mixing ratios at an urban site in Las Vegas, Nevada

Oxidation of benzene, toluene, ethylbenzene, and xylenes (BTEX) in air, of significance due to, for example, the potential for O3 formation, is believed to be initiated by OH attack on the ring (addition) or on the alkyl side chain (H abstraction). A series of ring-breaking reactions follows, with major products predicted to be alpha-dicarbonyls, simple aldehydes, and organic acids. To test this prediction, ambient air mixing ratios of aldehydes (formaldehyde, acetaldehyde, benzaldehyde, glyoxal, and pyruvaldehyde), along with some supporting BTEX data, were measured at an urban site in Las Vegas, NV. Samples were collected on sorbents and determined by chromatographic methods; mixing ratios were compared to ambient levels of CO, O3, and NOx. A meteorological analysis (temperature, wind speed, and wind direction) was also included. Statistically significant relationships were noted among the BTEX hydrocarbons (HCs) and among the photochemically derived species (e.g., O3, NO2, and some of the aldehydes), although there was seasonal variation. The observations are consistent with a common primary source (i.e., vehicular exhaust or fuel evaporation) for the BTEX compounds and a common secondary source (e.g., OH attack) for glyoxal and pyruvaldehyde.     

The Wahlund effect and the geographical scale of variation in the intertidal limpet Siphonaria sp.

Samples of Siphonaria sp. were collected between 1978 and 1982 from sites covering its known geographic range, from Kalbarri, Western Australia to Port Robe, South Australia. Geographic variation of 7 polymorphic enzymes was examined in this intertidal pulmonate limpet, and was found to be consistently small, indicating a large-scale influence of gene flow due to planktonic dispersal. Despite this large-scale uniformity, there is fine-scale genetic patchiness, which is repeated, rather than accumulated, on the larger scale. Throughout its geographic range, Siphonaria sp. shows deficits of heterozygotes for all 7 loci. The consistency among loci indicates that the causes of the deficits are populational, rather than locus-specific. A Wahlund effect, the departure from Hardy-Weinberg equilibrium due to mixing of individuals from groups with different allelic frequencies, is the simplest explanation of such deficits. The limited geographic variation of allelic frequencies, however, is grossly inadequate to produce these deficits through a Wahlund effect. Similarly, temporal variation in allelic frequencies in recruits does not explain the deficits. The largest contributor to a Wahlund effect appears to be binomial sampling variance among small local breeding groups. Thus, mixing of larvae on a scale of metres, rather than among geographical areas, apparently produces the deficits of heterozygotes.     

Urinary arsenic concentrations and speciation in Cornwall residents

Inorganic arsenic and its methylated metabolites were determined in urine from adults and children in Cornwall and from corresponding control groups in Glasgow. In the mineralised south-west of England, where it has been suggested that the highly enriched soil arsenic concentrations may at least be a cofactor in the increased incidence of skin cancer, urinary arsenic levels were, in general, only slightly elevated. The potential for increased intake of inorganic arsenic in Cornwall was, however, reflected in the more frequent occurrence of trivalent inorganic arsenic and monomethylarsonic acid in urine and, of especial significance, in two comparatively highly elevated sum of arsenic species concentrations of 48.7 and 20.8 g g^–1 creatinine recorded for two pre-school children. These findings are discussed with reference to recommended limits and pathways of exposure to inorganic arsenic.