Bioavailability, accumulation and effects of heavy metals in sediments with special reference to United Kingdom estuaries: a review

Using mainly United Kingdom estuaries as examples, various factors governing the bioavailability, bioaccumulation and biological effects of heavy metals in sediment-dominated estuaries are reviewed. Estuaries and metals primarily discussed include the Mersey (Hg, methylmercury; Pb, alkyllead), the Loughor (Cr, Sn), the Severn (Ag, Cd), the Fal (As, Cu, Sn, Zn), Poole Harbour (Cd, Hg, Se, tributyltin) and Southampton Water (tributyltin). Concentrations and bioavailabilities of metals in estuarine sediments depend on many different processes. Examples include (1) mobilisation of metals to the interstitial water and their chemical speciation, (2) transformation (e.g. methylation) of metals including As, Hg, Pb and Sn (3) the control exerted by major sediment components (e.g. oxides of Fe and organics) to which metals are preferentially bound, (4) competition between sediment metals (e.g. Cu and Ag; Zn and Cd) for uptake sites in organisms, and (5) the influence of bioturbation, salinity, redox or pH on these processes. Under field conditions, identification of dominant processes can be achieved by observing the goodness of fit between metal concentrations in ubiquitous deposit-feeding species and levels in various types of sediment extract over a wide spectrum of sediment types. Factors of more local importance are often indicated by the marked deviation of some points from otherwise excellent relationships. For example, points lying above the line relating tissue Sn concentrations in the clam Scrobicularia plana to those in 1 n HCl extracts of sediments were found to reflect the accumulation of tributyltin, a more readily bioavailable form of Sn. In the same species, unexpectedly high tissue-Cu concentrations were characteristic of very anoxic in sediments and tissue And As and Pb concentrations were suppressed in sediments having high concentrations of Fe oxides. Under field conditions, examples of deleterious effects on benthic organisms that can be attributed to specific metallic pollutants are comparatively rare. Effects of tributyltins from antifouling paints on oysters and neogastropods have been documented and their toxicity has undoubtedly led to environmental degradation in many UK estuaries and coastal areas. In estuaries contaminated with metal-mining wastes, the effects of Cu and Zn on species distribution can be observed, but they are generally less obvious than would be predicted from experimental data. Effects are ameliorated by the induction of metal tolerance mechanisms in some species and in others by the appearance of tolerant strains. The induction of metal detoxification systems involving the formation of granules or metal-binding proteins leads in some species to tissue concentrations that are orders of magnitude higher than normal. For example, high concentrations of Cd and Ag have been found in some species from the Severn Estuary, although there is no unequivocal evidence that either metal has caused deleterious effects on benthic populations. On the other hand, experimental studies with Ag, Cd, Cr, Cu, Hg and Zn show that they are toxic to some species at environmentally realistic levels. Since pollutants rarely occur singly, it is likely that in many moderately contaminated estuaries metals contribute to the stress to organisms caused by substances requiring detoxification. There has been much speculation over the years concerning the biomagnification of metals with increasing trophic levels along food chains. Whilst animals having higher metal concentrations than their prey are sometimes found, the only consistent evidence of biomagnification concerns methylmercury. When estuarine birds are considered, there are relatively few instances in which deleterious effects can unequivocally be attributed to metals or their compounds. However, the Mersey bird kill was attributable to alkyllead pollution from industry. Among other organometals, methylmercury has proved toxic to birds but, so far, no evidence for the toxicity of tributyltin has been reported. However, the compound may have affected bird populations through its effects on the abundance of prey organisms, particularly estuarine molluscs. Of the inorganic forms of metals, Pb in the form of shot has caused problems in many areas and Cd, Hg and Se are suspected of causing toxic effects. There is little field evidence that birds have been affected by Ag, As, Cr, Cu or Zn individually. On the other hand, it is difficult to exclude the possibility that, additively, these metals may produce a significant effect. In part, the lack of evidence reflects the fact that relatively little research has been done. There is scope for more work on metals and organometals in estuarine birds, particularly with regard to their metabolism and their effects on juveniles and individuals subjected to stresses such as starvation.     

The aggregation pheromone ofIps duplicatus and its role in competitive interactions withI. typographus (Coleoptera: Scolytidae)

Summary Ips duplicatus withI. typographus co-inhabiting Norway spruce (Picea abies (L.) Karst.) would benefit from a pheromone blend distinct from that of the larger competitorI. typographus. GC-MS analysis showed thatI. duplicatus males feeding in the host produced ipsdienol (Id),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt), andE-myrcenol (EM) and traces of 2-methyl-3-buten-2-ol (MB).I. duplicatus produced Id in approximately racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on day 2. Exposure ofI. duplicatus males to myrcene and -pinene resulted in the production of small amounts of Id, cV, tV, Mt, andtrans-pinocarveol, but not of EM. In laboratory bioassays with walking beetles, the pheromone component Id alone was weakly attractive while EM was inactive, but in binary combination with Id strongly synergized attraction. A combination of EM and Id at a release rate equivalent to 100–200 males was more attractive in the field than 70 unmated males in a spruce log. The addition of myrcene ( a suggested pheromone precursor of Id) to Id did not enhance trap caches, while addition of EM increased catches > 10-fold. Subtracting EM from a blend of Id, EM, cV and MB drastically reduced trap catches while subtraction of cV or MB or both had no significant effect. Addition of EM over a wide concentration range to the synthetic pheromone ofI. typographus did not reduce the attraction of females of this species in the laboratory. A two-species pheromone interaction field test releasingI. typographus pheromone components (MB + cV) at 10–1000 male equivalents (ME) andI. duplicatus pheromone (Id + EM) at 0, 10–1000 ME in all possible combinations showed both positive intraspecific dose-response effects and an interspecific inhibition. Higher release rates of EM appeared to inhibitI. typographus, especially males. In a tree colonization model, the response of the two competing species to their respective pheromones show a good separation during the mass-attack with a small initial cross-attraction. It remains to be shown whether either of the two pheromone systems have in fact evolved in the present sympatry, or if they are an incidental effect of ancestry of these phylogenetically distantIps.     

Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).     

Variation of leaf gland volatile oil within a population of sweet gale (Myrica gale) (Myricaceae)

Summary The leaf gland volatile oils of ten sweet gale plants from a Scottish population were extracted in early summer. The results differed notably from reports of other populations in respect of the sesquiterpenes, -elemenone and germacrone, which were major components of the volatile oil. Three dihydrochalcones were also detected in the volatile oil. Variation within the population existed, particularly with respect to the relative importance of germacrone. Five plants were resampled in late summer and exhibited a marked reduction in -elemenone, a lesser reduction in germacrone and changes in the proportions of some monoterpenes.     

Seasonal trend of fog water chemical composition in the Po Valley

Fog frequency in the Po Valley, Northern Italy, can be as high as 30% of the time in the fall-winter season. High pollutant concentrations have been measured in fog water samples collected in this area over the past few years. The combined effects of high fog occurrence and high pollutant loading of the fog droplets can determine, in this area, appreciable chemical deposition rates. An automated station for fog water collection was developed, and deployed at the field station of S. Pietro Capofiume, in the eastern part of the Po Valley for an extended period: from the beginning of November 1989 to the end of April 1990. Time-resolved sampling of fog droplets was carried out during all fog events occurring in this period, and chemical analyses were performed on the collected samples. Statistical information on fog occurrence and fog water chemical composition is reported in this paper, and a tentative seasonal deposition budget is calculated for H+, NH4+, NO3- and SO4(2-) ions. The problems connected with fog droplet sampling in sub-freezing conditions are also addressed in the paper.     

Observations of H2O2 and PAN in a rural atmosphere

Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants.     

Deposition of ozone to a mature spruce forest: measurements and comparison to models

Removal of ozone at terrestrial surfaces provides a major sink for tropospheric ozone and, therefore, a constraint on the peak concentrations achieved during photochemical episodes. This study reports results from 5 years of almost continuous measurements of vertical profiles of ozone and related meteorological variables over a mature spruce forest in Bavaria. Deposition velocities calculated from flux/gradient and eddy correlation flux measurements have been compared with estimates based on a resistance model and yield satisfactory agreement during fine weather conditions. The results also suggest that biogenic emissions of reactive hydrocarbons from the forest influence the vertical profile of ozone.     

Trace metals in interstitial waters from sandstones: acidic inputs to shallow groundwaters

There is some evidence from southern Britain that shallow groundwaters in non-carbonate lithologies may be affected by acidic deposition. To investigate this, interstitial water profiles down to 12 m have been obtained from unsaturated sands or semi-consolidated sandstones from the Folkestone Beds (Lower Greensand) of Surrey and the Sherwood Sandstone of the West Midlands. The pH of the interstitial waters generally increased with depth and reflected an increase in the base saturation of the exchange complex. Beneath the highly acidic surface soil horizons (pH 3.0-3.5), interstitial waters with a pH of 4.0-4.5 were found down to depths of several metres. The pH progressively increased to around pH 5.5 because of base cation desorption and the weathering of silicate minerals. High concentrations of aluminium (10-20 mg litre(-1)) and other metals (Fe, Mn, Cu, Ni, Co, Zn, Be) were found in the interstitial water in the upper unsaturated zone. Most metal concentrations were strongly pH-dependent but also reflected the geochemical characteristics of the parent sands or sandstones. H+ and trace element concentrations were slightly higher beneath areas of afforestation than beneath heathland. The downward fluxes of solutes have been estimated using rainfall-derived chloride as a non-reactive solute. The profiles retain a record of 10-20 years input allowing the past inputs from SO4 and other species to be estimated using solute/chloride ratios. Cation exchange sites are probably depleted over a period of decades and there can be a significant decrease in the unsaturated zone pH as a result of increased or sustained acidic deposition. The shallow groundwater environment (0-15 m) in non-carbonate terrains is therefore a sensitive environment where high metal concentrations may be generated and may ultimately lead to water quality problems in shallow water supplies.