Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs

Air-vegetation exchange of POPs is an important process controlling the entry of POPs into terrestrial food chains, and may also have a significant effect on the global movement of these compounds. Many factors affect the air-vegetation transfer including: the physicochemical properties of the compounds of interest; environmental factors such as temperature, wind speed, humidity and light conditions; and plant characteristics such as functional type, leaf surface area, cuticular structure, and leaf longevity. The purpose of this review is to quantify the effects these differences might have on air/plant exchange of POPs, and to point out the major gaps in the knowledge of this subject that require further research. Uptake mechanisms are complicated, with the role of each factor in controlling partitioning, fate and behaviour process still not fully understood. Consequently, current models of air-vegetation exchange do not incorporate variability in these factors, with the exception of temperature. These models instead rely on using average values for a number of environmental factors (e.g. plant lipid content, surface area), ignoring the large variations in these values. The available models suggest that boundary layer conductance is of key importance in the uptake of POPs, although large uncertainties in the cuticular pathway prevents confirmation of this with any degree of certainty, and experimental data seems to show plant-side resistance to be important. Models are usually based on the assumption that POP uptake occurs through the lipophilic cuticle which covers aerial surfaces of plants. However, some authors have recently attached greater importance to the stomatal route of entry into the leaf for gas phase compounds. There is a need for greater mechanistic understanding of air-plant exchange and the 'scaling' of factors affecting it. The review also suggests a number of key variables that researchers should measure in their experiments to allow comparisons to be made between studies in order to improve our understanding of what causes any differences in measured data between sites.     

A basidiomycete isolated from the skeleton of<Emphasis Type="Italic"> Pocillopora damicornis</Emphasis> (Scleractinia) selectively stimulates short-term survival of coral skeletogenic cells

Endolithic fungi bore through the extracellular calcium carbonate skeleton of reef-building scleractinian corals, both healthy and dead, and effect net erosion of coral reefs. Potential fungal interactions with coral tissue were investigated using an in vitro approach suggested by earlier observations of skeletal repair cones at the site of fungal perforation in Porites sp. A fungal strain was isolated from the skeleton of a long-term culture of healthy, tissue-covered, Pocillopora damicornis Linnaeus colonies maintained in a recirculating system in Monaco. As coral soft tissue spontaneously dissociated in vitro, the skeleton became exposed and hyaline hyphae emerged radially from 15% of the total clipped branches. In this study, which was performed between January 2001 and March 2003, 35 skeleton–hypha explants were embedded in agar-based solid medium, yielding 60% hyphal growth. A fungal strain (F19-3-1) of the dominant (80%) morphology was isolated and propagated in agar-based solid medium. The strain was identified by 18S and 26S rDNA gene sequence analysis as a basidiomycete in the genus Cryptococcus. Co-cultures were used to provide experimental exposure of coral soft tissue to the fungus. The fungus extended the survival of coral cells by 2 days, selectively maintaining skeletogenic cell types. This effect may be interpreted as stimulation by the fungus of a short-term coral defense response.Communicated by J.P. Grassle, New Brunswick     

Cloning and expression of high choriolytic enzyme,a component of the hatching enzyme system,during embryonic development of the marine ornamental fish<Emphasis Type="Italic"> Chrysiptera parasema</Emphasis>

In the present study, a cDNA for the hatching enzyme of a marine tropical fish, Chysiptera parasema, was cloned. This is the first demonstration of hatching enzyme cDNA from a marine tropical fish. The amino acid (aa) sequence deduced from the cDNA consisted of an 18-aa signal sequence, a 53-aa propeptide sequence and a 196-aa mature enzyme portion, having a consensus active site sequence for astacin family proteases. Phylogenetic analysis showed that the C. parasema enzyme was included in the clade of HCEs (high choriolytic enzymes), one of the hatching enzymes of freshwater fishes such as medaka (Oryzias latipes), masu salmon (Oncorhynchus masou) and zebrafish (Danio rerio), but not in the group of LCEs (low choriolytic enzymes), another type of hatching enzymes identified in the medaka. The developmental expression patterns of the C. parasema HCE gene were highly similar to that of the medaka HCE gene. The results suggested that the hatching enzyme system is highly conserved between these marine and freshwater fish species.Communicated by R. Cattaneo-Vietti, Genova     

Behavioural and physiological responses of the Norway lobster,<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> (Crustacea: Decapoda), to sulphide exposure

The Norway lobster, Nephrops norvegicus, is moderately tolerant of sulphide [the lethal time to 50% mortality (LT₅₀) was 22.5 h when exposed to 500 M sulphide] but, whenever possible, it attempts to avoid the presence of sulphide in its immediate vicinity. Any sulphide entering the animal is oxidized to thiosulphate, which accumulates in the haemolymph and in the tissues. During exposure to low concentrations of sulphide, the rate of oxygen consumption is maintained or even enhanced even though the lobsters become quiescent. The apparent increase in oxygen consumption is probably due to the oxidation of sulphide to thiosulphate. At higher concentrations, oxygen consumption decreases, perhaps because of the inhibitory effect of sulphide on electron transport, and N. norvegicus resorts to anaerobic metabolism as indicated by the accumulation of lactate in the haemolymph and in the tissues.Communicated by L. Hagerman, Helsingør     

Integrative Evaluation of the Ecological Quality of Metalliferous Streams (Chalkidiki, Macedonia, Hellas)

The present study reports on a year-long (November 1997-November 1998) study of water quality in streams of the Olympias and Skouries areas of Chalkidiki (Hellas), subject to past and present mining activities. Benthic macroinvertebrates were collected from 18 sampling sites at five sampling intervals, while several physicochemical parameters of the water (D.O., pH, temperature, nutrients etc.) were also measured. Five European biotic indices and scores and two multivariate statistical methods (CANOCO, FUZZY) were applied to the macroinvertebrate data. The concentration of various trace metals in the water, sediment, fish and crustaceans were also measured. Most sampling stations exhibited a highly diverse macroinvertebrate fauna during the whole year. However, a slight amelioration of water quality was observed during the high-flow period (winter and early spring), regarding diversity of several invertebrate groups, especially pollution-sensitive families, which decreased. The European biotic indices and scores proved to be relatively ineffective in describing water quality and it is suggested that an Hellenic biotic indice or score should be created. The bioaccumulation studies indicated variable effects of trace metals and organic load on macroinvertebrates according to the degree of load.     

Effect of Cage Design on Growth of Transplanted Asian Clams: Implications for Assessing Bivalve Responses in Streams

This study was designed to determine whether survivorship and growth of Asian clams (Corbicula fluminea [Müller]) differed significantly between two types of field enclosures. Enclosures were either flexible mesh bags or rigid cages (hereto after referred as bioboxes) designed to homogenize substrate among study sites and accommodate Asian clam feeding mechanisms. For 96d, cages remained at 12 Clinch River (CR), Hurricane Fork (HF), and Dump's Creek (DC) sites upstream and downstream of a coal-fired power plant discharge, coal mining effluent, and coal combustion-related disposal facilities in Carbo, Virginia. Although survivorship was not significantly different between cage types, mean growth of clams in bioboxes was significantly greater overall (p = 0.0157). Despite the difference in growth between the two cage types, both confirmed significant reductions of survivorship and growth directly below the power plant discharge. Additionally, coefficient of variance values for biobox growth data were reduced at most study sites (averages of 16% for bioboxes versus 19% for mesh bags). Our results have implications toward strengthening weight-of-evidence approaches used to link impairment of transplanted bivalves to environmental contaminants. More importantly, these results suggest that ecotoxicological impairment of bivalves transplanted downstream of the coal-fired power plant discharge functioned independently of site-specific substrate provisions.     

MTBE oxidation byproducts from the treatment of surface waters by ozonation and UV-ozonation

In recent years, there has been considerable concern over the release of methyl tert-butyl ether (MTBE), a gasoline additive, into the aquifers used as potable water sources. MTBE readily dissolves in water and has entered the environment via gasoline spills and leaking storage tanks. In this paper, we investigate ozonation and UV-ozonation for treatment of MTBE in contaminated drinking water sources. We report the test protocol and results of using solid-phase microextraction (SPME) to determine the level of MTBE and its oxidation byproducts in samples drawn from laboratory-scale ozone and UV-ozone reactors being evaluated at a US EPA research facility. Analysis of a prepared MTBE standard indicated a detection limit on the order of 0.1 microgl(-1) with a repeatability of +/-0.4%. Results show that the overall rate of removal of MTBE via UV-ozonation in a relatively turbid surface water (15 ntu) is twice that of ozonation alone. In addition, GC-MS analysis of decomposition products showed that tert-butyl formate (TBF), methyl acetate, butene, acetone, and acetaldehyde were produced by both processes. TBF and butene reach similar maximum yields from the two processes, but are more efficiently degraded by UV-ozonation treatment. This indicates that these treatment processes also degrade these byproducts. In contrast, the remaining byproducts (methyl acetate, acetone, and acetaldehyde) are formed at similar levels during treatment, but are not degraded once formed. These byproducts may be resistant to hydrogen abstraction by hydroxyl radical.     

Characterisation of the dilute HCl extraction method for the identification of metal contamination in Antarctic marine sediments

A regional survey of potential contaminants in marine or estuarine sediments is often one of the first steps in a post-disturbance environmental impact assessment. Of the many different chemical extraction or digestion procedures that have been proposed to quantify metal contamination, partial acid extractions are probably the best overall compromise between selectivity, sensitivity, precision, cost and expediency. The extent to which measured metal concentrations relate to the anthropogenic fraction that is bioavailable is contentious, but is one of the desired outcomes of an assessment or prediction of biological impact. As part of a regional survey of metal contamination associated with Australia's past waste management activities in Antarctica, we wanted to identify an acid type and extraction protocol that would allow a reasonable definition of the anthropogenic bioavailable fraction for a large number of samples. From a kinetic study of the 1 M HCl extraction of two Certified Reference Materials (MESS-2 and PACS-2) and two Antarctic marine sediments, we concluded that a 4 h extraction time allows the equilibrium dissolution of relatively labile metal contaminants, but does not favour the extraction of natural geogenic metals. In a regional survey of 88 marine samples from the Casey Station area of East Antarctica, the 4 h extraction procedure correlated best with biological data, and most clearly identified those sediments thought to be contaminated by runoff from abandoned waste disposal sites. Most importantly the 4 h extraction provided better definition of the low to moderately contaminated locations by picking up small differences in anthropogenic metal concentrations. For the purposes of inter-regional comparison, we recommend a 4 h 1 M HCl acid extraction as a standard method for assessing metal contamination in Antarctica.     

Toxicities and tolerances of Cd, Cu, Pb and Zn in a primary producer (Isochrysis galbana) and in a primary consumer (Perna viridis)

Studies on toxicities and tolerances of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in the brown alga Isochrysis galbana and in the green-lipped mussel Perna viridis were conducted by short-term bioassays using endpoints growth production and mortality, respectively. The 5-day EC(50) and 24-h LC(50) of these heavy metals were determined in the brown alga and mussel, respectively. The EC(50) values calculated for the alga were 0.74 mg/l for Cd, 0.91 mg/l for Cu, 1.40 mg/l for Pb and 0.60 mg/l for Zn. The LC(50) values for the mussels were 1.53 mg/l for Cd, 0.25 mg/l for Cu, 4.12 mg/l for Pb and 3.20 mg/l for Zn. These LC(50) values were within the concentration ranges as reported by other authors who used P. viridis as the test organism. Based on these EC(50) and LC(50) values, the alga was most sensitive to Zn, followed by Cd, Cu and Pb while the mussel was most sensitive to Cu, followed by Cd, Zn and Pb. Differences in the trophic levels, metal handling strategies, biology and ecology of the primary producer (brown alga) and the primary consumer (mussel) are believed to be the plausible causes for the different toxicities and tolerances of the metals studied.     

Assessment of contamination by heavy metals and petroleum hydrocarbons in sediments of Montevideo Harbour (Uruguay)

As part of the first environmental assessment within Montevideo Harbour, in summer and winter of 1998, sediments samples were collected at eight locations to determine the spatial distribution of anthropogenic pollutants. Muddy sediments with high organic matter content dominate the study area. Heavy metal levels indicated that sediments were highly polluted with Zn (overall mean: 312+/-102 microg g(-1) dry sediment), Pb (85+/-31), Cu (89+/-25), Cr (162+/-62), and Hg (0.63+/-0.3) and moderately with Ni (30+/-2) and Ag (1.2+/-0.4). Depending on location and season, aliphatic hydrocarbons reached from 21 to 120 microg g(-1), while the unresolved complex mixture represented up to 76% of the total aliphatic fraction. Total PAH concentrations ranged from 1.56 to 90.44 microg g(-1); except at one location, petroleum derivatives were identified as main local source. The results pointed out that almost all the harbour area presented some substances that can cause adverse biological effects, especially in the inner region where all metals are above PEL levels. Principal components analysis confirmed that the inner harbour region is most severely affected by the pollutants and it was possible to differentiate three regions according to their environmental quality.