Oil pollution monitoring in the Lagoon of Venice using the mussel Mytilus galloprovincialis

Gas chromatographic analyses of mussels, Mytilus galloprovincialis, from different areas of the Lagoon of Venice show that these organisms contain a very complex mixture of hydrocarbons attributable to fuel oil contamination. The measured amounts normally range from 0.8 to 8.7 mg/100 g wet weight, but values as high as 22.0 mg/100 g have been recorded. This high value indicates a saturation limit for these organisms which is considerably higher than those values normally found in mussels from the lagoon. The aliphatic hydrocarbon levels in mussels are related to distance from pollution sources and to the degree of exchange between the sea and the area sampled. On the basis of this relationship between overall hydrocarbon pollution load and level of contamination of M. galloprovincialis, it appears that this bivalve might be effectively utilized as a self-integrating monitoring index of oil pollution in the wasters of the lagoon.     

Simulation tools to support bathing water quality management: Escherichia coli bacteria in a Baltic lagoon

Insufficient hygienic water quality and bathing prohibitions are still a serious problem in the Szczecin Lagoon (southern Baltic). In our study we focus on the southern lagoon coast and analyse the causes and consequences of high Escherichia coli bacteria concentrations. For this purpose we carry out laboratory experiments on the behaviour of E.coli in the lagoon, a literature review and apply a three-dimensional flow model together with a Lagrangian particle tracking routine. Three major E.coli sources, the Uecker river, the wetlands with cattle as well as sea gulls with bathing and fisheries were allocated, quantified and compiled into an emission scenario. This serves as input for transport simulations under different wind conditions and for the development of a spatial contamination map. Reasons for high E.coli concentrations in the lagoon are a permanent supply from different sources and the special environmental situation in the lagoon. The availability of organic matter, either in form of reed stems or as muddy sediments, has a positive effect on bacteria survival. Very important, too, are the prevailing wind and flow conditions, which cause water and organism transport in narrow ribbons along the coastline and promote near-shore accumulations. Even in our shallow lagoon, the application of a 3D-model is beneficial. Heavy rains are, very likely, responsible for the outstanding high total-coliform concentrations of 11,000?cfu/100?ml on August 21, 2006. The model system proved to be a valuable tool for spatial analysis and is suitable to support the development of bathing water profiles according to the EU Bathing Water Directive (2006/7/EC).     

Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats

Shell growth rate is an important component of fitness in bivalve molluscs. Using the parameter computed from the von Bertalanffy growth equation, we quantitatively compared rates of annual shell grwoth among the hard clams Mercenaria mercenaria, M. campechiensis, and their hybrids sampled from a variety of habitats in the Indian River lagoon, Florida, USA, a zone of species overlap and natural hybridization. Our results indicate that the classical paradigm describing hard clam growth, in which growth rate is fastest in M. campechiensis, intermediate in hybrids, and slowest in M. mercenaria is not supported in the Indian River lagoon. Instead, M. campechiensis has a growth advantage in deep-water habitats in the northern section of our study area. In the central and southern sections of our study area, hybrids have a growth advantage over M. mercenaria in shallow-water habitats, but M. mercenaria has a growth advantage over hybrids in deep-water habitats. In all other sampled habitats, either growth rate among genotype classes is equal, or M. mercenaria has a growth advantage. This complex relationship between genotype and habitat-specific growth provides a mechanism for selection to act on hard clams in the Indian River.     

Trace metals accumulation in soil irrigated with polluted water and assessment of human health risk from vegetable consumption in Bangladesh

Trace metals accumulation in soil irrigated with polluted water and human health risk from vegetable consumption was assessed based on the data available in the literature on metals pollution of water, soil, sediment and vegetables from the cites of Bangladesh. The quantitative data on metal concentrations, their contamination levels and their pollution sources have not been systematically gathered and studied so far. The data on metal concentrations, sources, contamination levels, sample collection and analytical tools used were collected, compared and discussed. The USEPA-recommended method for health risk assessment was used to estimate human risk from vegetable consumption. Concentrations of metals in water were highly variable, and the mean concentrations of Cd, Cr, Cu and As in water were found to be higher than the FAO irrigation water quality standard. In most cases, mean concentrations of metals in soil were higher than the Bangladesh background value. Based on geoaccumulation index (I _geo) values, soils of Dhaka city are considered as highly contaminated. The I _geo shows Cd, As, Cu, Ni, Pb and Cr contamination of agricultural soils and sediments of the cities all over the Bangladesh. Polluted water irrigation and agrochemicals are identified as dominant sources of metals in agricultural soils. Vegetable contamination by metals poses both non-carcinogenic and carcinogenic risks to the public. Based on the results of the pollution and health risk assessments, Cd, As, Cr, Cu, Pb and Ni are identified as the priority control metals and the Dhaka city is recommended as the priority control city. This study provides quantitative evidence demonstrating the critical need for strengthened wastewater discharge regulations in order to protect residents from heavy metal discharges into the environment.     

UV-absorbing substances in zooxanthellate and azooxanthellate clams

The effects of UV-A and UV-B radiation on photosynthesis of zooxanthellae within the siphonal mantle of the giant clam, Tridacna crocea, and in isolation were studied. While UV-B irradiation (2.4 W m⁻², 20 min) completely suppressed photosynthesis of the isolated zooxanthellae, it had little effect on their photosynthetic ability if they were irradiated while within the siphonal mantle of the host tissue. Chemical analysis of the siphonal mantle of T. crocea showed the presence of significant amounts of mycosporine-like amino acids (MAAs), which absorb UV-A and -B light. However, no MAA was detected in the isolated zooxanthellae. MAAs were concentrated in the siphonal mantle and kidney tissues in comparison with other tissues. In the siphonal mantle, MAA concentrations were the highest in the outermost surface layer where most of the zooxanthella cells resided. This indicates that the zooxanthellae are protected from UV radiation by a screen of concentrated MAAs in the host clam. Aside from T. crocea, significant amounts of MAAs were found not only in other zooxanthellate clams, such as T. derasa, Hippopus hippopus, Colculum cardissa and Fragum unedo, but also in a closely related azooxanthellate clam, Vasticardium subrugosum. On the other hand, no MAA was detected in any of the zooxanthellae from these zooxanthellate clams. No MAA was detected in the tissues of a deep-sea bivalve, Calyptogena soyoae. Although MAAs seem to block strong UV radiation in the shallow-water clam, they are probably not essential for the clam's life in the dark. MAAs in shallow-water clams may be derived from food and accumulated in their tissues, especially in the siphonal mantle and kidney. Received: 29 November 1996 / Accepted: 13 January 1997     

Assessment of the aquatic biodiversity of a threatened coastal lagoon at Bimini, Bahamas

Coastal biodiversity is threatened worldwide by both direct and indirect anthropogenic activities. To more effectively manage and protect coastal biodiversity, accurate assessments of genetic, species, and ecosystem level diversity are required. We present the results from an assessment of the aquatic species diversity of a small (3?km²), shallow, mangrove-fringed Bahamian lagoon (the North Sound) subject to ongoing anthropogenic development. The assessment was conducted through a collation of field observations and data in published literature. We found that eight angiosperm species, 30 macroalgal species, and 370 animal species (including 95 fishes, 69 arthropods, 56 birds, and 45 mollusks) were documented within the lagoon. At least 11 of these species are of conservation concern, such as the critically endangered smalltooth sawfish (Pristis pectinata) and hawksbill turtle (Eretmochelys imbricata). Comparisons of community similarity indicated that the North Sound has a relatively distinct fauna and flora, but available data suggest that the species found there are most similar to those found in nearby habitats in Cuba. The lagoon forms a key nursery habitat for many species, including lemon sharks (Negaprion brevirostris), Caribbean spiny lobsters (Panulirus argus), and queen conch (Strombas gigas). Recently, the lagoon was included as part of a new marine protected area (MPA), but much of the habitat has already experienced considerable anthropogenic disturbance and the MPA boundaries have yet to be established. We have therefore analyzed the lagoon biodiversity and expect the data presented here to serve as a baseline for future comparisons.     

Sea otter foraging on deep-burrowing bivalves in a California coastal lagoon

Sea otter, Enhydra lutris, predation had no detectable effect on abundance and size distribution of deep-burrowing bivalve prey in the Elkhorn Slough, California, USA. Up to 23 otters were present for 6 mo of the study period (March 1984 through April 1985). This is in contrast to previous studies of sea otter predation, especially on the shallow-burrowing Pismo clam Tivela stultorum, which can be found along the wave-exposed coast near the slough. The deep-burrowing clams Tresus nuttallii and Saxidomus nuttalli made up 61% of the prey taken in the slough, and are more difficult for otters to excavate than Pismo clams. The occurrence of foraging otters was highest in an area where the two bivalve prey were extremely abundant (18 individuals m^–2). However, the otters did not selectively prey on the largest clams available within the study sight, but foraged preferentially in a patch of smaller individuals where bivalve burrow depth was restricted by the presence of a dense clay layer. This foraging strategy maximized the amount of prey biomass obtained per unit volume of sediment excavated. Our findings suggest that in soft-sediment habitats deep-burrowing bivalves may be more resistant to otter predation than shallower burrowers.     

Mechanical clam dredging in Venice lagoon: ecosystem effects evaluated with a trophic mass-balance model

Harvesting of the invasive Manila clam, Tapes philippinarum, is the main exploitative activity in the Venice lagoon, but the mechanical dredges used in this free-access regime produce a considerable disturbance of the lagoon ecosystem. An ecosystem approach to study the complex effects of clam harvesting was implemented using a trophic mass-balance model. The trophic relations in the ecosystem were quantified with a mixed trophic impact analysis and further evaluated by considering different explanations for the " Tapes paradox", which consists of the apparent population enhancement of Manila clams by dredging and the apparent nutritional advantages that this species receives from re-suspended organic matter. The key-role played by this introduced species is highlighted by a network analysis that indicates a "wasp-waist control" of the system by Manila clams. The model constructed to characterise the present state of the Venice lagoon ecosystem is compared with models produced for a reconstructed past lagoon and a projected future lagoon. The future model was obtained by simulating the elimination of clam dredging in 10 years. The three different models were compared using thermodynamic and informational indices. Simulating the elimination of clam dredging produced a 33% increase in artisanal fishery catches, carried out by means of static gears, even with no change in fishing effort. These simulations also forecast an increase in the mean trophic level of the artisanal fishery catches as a positive effect of eliminating mechanical clam harvesting.     

Sensitivity of modelled gross primary productivity to topographic effects on surface radiation: A case study in the Cotter River Catchment, Australia

Gross primary productivity (GPP) is a critical response variable for many environmental problems, including terrestrial carbon accounting and the calculation of catchment water balances. Various approaches for modelling GPP have been developed and applied at continental and landscapes scales, but little attention has been given to the sensitivity of GPP to the spatial scale of its driving variables. A key driving variable is surface radiation (R_s) which is influenced by both meso-scale factors (latitude, time of year, cloudiness) and the topographic variables of slope, aspect and horizon shading. We compared the sensitivity of modelled GPP to two different sources of surface radiation (R_s): (1) the ANUCLIM method which only captures the meso-scaled factors; and (2) the SRAD method which incorporates the topographic effects GPP was calculated using the radiation use efficiency (RUE) model (Roderick et al., 2001) to discern general patterns of vegetation productivity at a sub-catchment (i.e. sub-water shed) scale. The radiation use efficiency approach uses the normalized difference vegetation index (NDVI) derived from satellite data (MODIS TERRA), along with estimates of solar radiation at the top of the atmosphere (R_o) and canopy (R_s). In this approach, R_o and R_s capture the influence of diffuse irradiance in canopy photosynthesis and vegetation productivity respectively. This research showed that R_s calculated using the SRAD program provides important discrimination of GPP regimes at a sub-catchment scale, as the result of minimum and maximum daily radiation varying between shaded and exposed surfaces. However, mean daily radiation at a whole-of-catchment scale did not differ between the two sources as the differences in the minimum and maximum daily values tend to cancel each other out. Applications of GPP models therefore need to consider whether topographic factors are important and select the appropriate source of R_s values. GPP models should also reflect understanding of radiation use efficiency. However, further research is required especially with respect to the influence of water stress on plant response.     

Sessile and non-sessile morphs of Geodia cydonium (Jameson) (Porifera, Demospongiae) in two semi-enclosed Mediterranean bays

Morphological plasticity and ecological aspects of the demosponge Geodia cydonium (Jameson) were studied from seasonal samples collected over 1 year in two semi-enclosed Mediterranean bays of the Southern Italian coast (Marsala lagoon and Porto Cesareo basin). Sponge specimens present two morphs: sessile and non-sessile, both of which showed constant size distribution and density over the studied year. Sessile specimens were larger in size than non-sessile ones. This feature is particularly evident at Porto Cesareo, where these sponges have a more compact skeletal network than at Marsala (evident both in the cortical spicule size and sponge silica content). Sessile specimens adhere to hard rocky substrates (Porto Cesareo) or phanerogam rhizomes (Marsala); non-sessile ones occur on soft bottom areas. Several morphological and structural features of the non-sessile forms differ in the two environments, but the difference in body shape seems to play the most relevant role in enhancing the colonization of incoherent substrates. Indeed, at Marsala, where the large amount of silt and clay determines the occurrence of a markedly reduced anoxic layer just below the surface of the sediment, non-sessile specimens of G. cydonium are fairly spherical and thus able to roll, dragged by slow circular currents. In addition, the usual association with the red alga Rytyphlöea tinctoria, which almost constantly forms a thick and continuous layer around the sponge, allows them to avoid contact with the substrate. The non-sessile specimens from Porto Cesareo inhabit sandy soft bottoms and are flattened. In such an environment, affected by moderate wave turbulence, the flattened shape widens the contact surface between the body and the substrate, thereby reducing the risk of stranding. The evident signs of abrasion, provided by scanning electron microscopy investigations, on both cortical spicules and outermost sponge surface suggest that sponges rub on the bottom. Sediment, epibiontic organisms, and the phanerogam leaves protect this sciaphilous sponge from high solar radiation, allowing the specimens to live in these shallow environments.     

A stochastic bioeconomic model for the management of clam farming

The Manila clam Tapes philippinarum is one of the most important commercial mollusc species in Europe. Intensive clam farming takes place in several coastal lagoons of the Northern Adriatic Sea, supporting local economy but raising the problem of the environmental sustainability of this activity. In this work, we propose a bioeconomic model that provides guidelines for an efficient management of intensive clam farming. Clam demography is described by a stochastic model of growth and survival, accounting for the effect of water temperature, seeding substratum and density dependence of vital rates. The model is calibrated on and applied to the case of Sacca di Goro, a lagoon located in the Po River Delta (Northern Italy). We consider two distinct management criteria: the optimisation of the marketable yield and the optimisation of monetary benefits, respectively. The use of a stochastic formulation allows us to reveal the existing trade-off between maximizing the median yield or profit and minimizing its variance. A Pareto analysis shows that seeding in spring or fall on sandy substrata and harvesting 18 months later provides the best compromise between these two contrasting objectives, maximizing profits while minimizing the associated uncertainty level. Finally, we show that seeding clams at high densities (more than 750 clams m⁻² on muddy substrata and more than 1500 elsewhere) can have not only a potentially negative impact on the ecological sustainability of clam farming, but also a negative economic effect.     

New methodological strategies for detecting bacterial indicators

The development of monitoring strategies for the early warning of seawater pollution, with particular reference to faecal and hydrocarbon contamination, has been the specific goal of research carried out within the Cluster 10-SAM (Advanced Systems for Coastal Marine Monitoring) Project, funded by the Italian Ministry for University and Scientific Research. Advanced analytical approaches have been designed and applied to detect bacterial species that have been selected as potential indicators of pollution in seawater samples. We report the results obtained using the fluorescent antibody and enzymatic assays for the detection of Escherichia coli, and a real-time PCR protocol for monitoring marine areas for hydrocarbon pollution. Immunofluorescence and enzymatic methods revealed the occurrence of different faecal pollution levels, reaching 10⁵ E. coli cells 100 ml^?1 in the Straits of Messina. Real-time PCR results corresponded to the different degree of oil pollution of the analysed samples. The specificity and speed make these methods promising for the detection and evaluation of marine pollution.     

Modelling radiative balance in a row-crop canopy: Cross-row distribution of net radiation at the soil surface and energy available to clusters in a vineyard

Distribution of energy at the soil surface in a row-crop influences mainly soil temperature and water content, and therefore root activity, nitrogen mineralization and within canopy air temperature, which all affect plant physiology. In the case of a vineyard, it is also closely related to the energy available to the berries and therefore most influential for fruit quality. The aim of this study was to develop a simplified model of available energy distribution at the soil surface and at the bottom of the rows, where most of the clusters are located. Such a model would be helpful for optimising some aspects of row-crop management like training system choice, row geometry, leaf area density, and soil surface maintenance practices.The model simulated radiation balance at the soil surface, split up into downward and upward short- and long-wave fluxes. Row shadows were calculated at any point of the inter-row space, in interaction with actual row geometry and simplified porosity distribution within row volume. All hemispheric radiations (long-wave and diffuse solar radiation) were calculated according to view factors between the row and soil surfaces. Input variables were therefore incoming solar radiation over the canopy, air temperatures near the row walls and soil surface temperatures. Parameters were row geometry, dimensions and porosities.The model was validated in a 7 years old Merlot vineyard in the Médoc area, by comparing model predictions to measured net radiation (Rns) at five positions above the inter-row soil surface. Along the row sampling was achieved by a moving device carrying the net-radiometers. Structure of the vegetation was kept constant during the experiment and gap fraction parameters were derived from pictures of shadows at the soil surface. Since Rns measurements are impracticable directly at the soil surface and horizontal distribution of Rns is heterogeneous, comparison was performed by calculating net radiation at the actual measurement height which was close to average cluster height.Model prediction agreed with field measurement in most conditions, which suggests that all short- and long-wave radiation fluxes, as well as interactions with the canopy structure, were well described. Rns, energy available to clusters, and soil surface temperature variations were all mainly driven by shading due to the rows. Coupling the model to soil heat transfer and convective fluxes to the atmosphere models will help forecasting soil temperature distribution at the surface and in depth as well as canopy microclimate. The model will also be an essential part of a more elaborate model of cluster microclimate, a key determinant of berry quality.     

Sediments distribution of trace metals in a coastal lagoon (Southern Sardinia,Mediterranean Sea): assessment of contamination and ecological risk

Coastal lagoons are subject to several sources of contaminations. To shade light on the contamination level of the Santa Gilla lagoon (Tyrrhenian Sea) we investigated the spatial distribution of Cr, Ni, Pb, Zn and Hg in sediments and their correlation with grain size and organic matter contents. Moreover, sediment contamination levels and the ecological risk associated with metal concentration were assessed using different abiotic indicators. The lagoon is characterised by low levels of contamination, with exceptions for Pb and Hg, whose distribution reflects the position of an old chlor-alkali plant and that of an airport. These results indicate that the restoration put in place 30 years ago have not reached the expected target and that the presence of the airport deserves further attention. In the outer section of the lagoon, where clam fishery occurs, we observed low levels of contamination suggesting that such artisanal fishery could somehow help mobilising metals. We conclude that the area exposed to Hg pollution, though tentatively restored, still suffers of a potential risk of ecosystem deterioration. We pinpoint that further investigations on the mobility, bioavailability and toxicity of metals are needed to finally address the actual impairment of the Santa Gilla lagoon.     

Population differences in nerve resistance to paralytic shellfish toxins in softshell clam, <Emphasis Type="Italic">Mya arenaria</Emphasis>, associated with sodium channel mutations

The softshell clam, Mya arenaria, is a commercially important bivalve with wide latitudinal distribution in North America. Populations of clams with a history of repeated exposure to toxic Alexandrium spp. have developed a natural resistance to the paralytic shellfish toxins (PSTs) produced by these algae. An association between PST resistance in individual clams and a single mutation in the saxitoxin (STX) binding region of the α-subunit of the voltage-gated sodium (Na⁺) channel gene was previously identified. Here we establish that more than one mutation associated with nerve resistance to STX occurred at this locus. Both cDNA from mRNA and genomic DNA sequences from individual clams are identical demonstrating that both alleles are expressed simultaneously. In addition, one resistant allele per individual is sufficient to confer neural resistance to STX even though heterozygous individuals show an intermediate level of resistance to STX in in vitro nerve trunk assays.     

Paralytic shellfish toxins sequestered by bivalves as a defense against siphon-nipping fish

Saxidomus giganteus (butter clams), are known to sequester diet-derived paralytic shellfish toxins (PST), highly potent neurotoxins, in their siphons. Captive staghorn sculpins (Leptocotus armatus), a marine fish species known to crop bivalve siphons, developed a significant aversion to siphons from toxic but not non-toxicS. giganteus following a single conditioning feeding of toxic siphon tissues. Control fish showed no aversive response to siphons from non-toxicS. giganteus during 11 feeding sessions over 56 d. Aversive and non-aversive behavior varied with the toxicity of the siphons, but not with the geographic origin of the clams. Both experimental and control fish ate freely and showed no aversion to siphons from toxic littleneck clams (Protothaca staminea). Littleneck clams, unlikeS. giganteus, retain PST in their visceral mass but not in their siphons. Both toxic and non-toxicS. giganteus extended their siphons significantly more often and higher above the sediment surface during dark hours, but toxicS. giganteus extended their siphons higher than non-toxic individuals. These results support the hypothesis that siphon-nipping by fish may have selected for the retention of PST in butter clam siphons as a chemical defense.     

Effect of streambed bacteria release on E. coli concentrations: Monitoring and modeling with the modified SWAT

Streambed sediment has been attracting attention as a reservoir for bacteria, including pathogenic strains. Soil and Water Assessment Tool (SWAT) has been augmented with a bacteria transport subroutine in SWAT2005 in which bacteria die-off is the only in-stream process. The purpose of this study was to develop the partial model of sediment-associated bacteria transport in stream and to evaluate the potential significance of streambed Escherichia coli (E. coli) release and deposition within the SWAT microbial water quality simulations. Streambed E. coli release and deposition were simulated based on the sediment resuspension and deposition modules in SWAT. The modified SWAT was applied to the Little Cove Creek watershed, Pennsylvania, which has forestry and dairy pasture landuses. Temporal changes in sediment E. coli concentrations were derived from monitoring data rather than from a streambed bacteria population model. Sensitivity analyses and calibrations were separately conducted for both hydrologic and bacteria parameters. Hydrologic calibration characterized soils in the watershed as pervious and thus the surface runoff was only moderately contributing to the streamflow. However, the surface runoff carried large numbers of E. coli to the stream, and sediment resuspension contributed to the persistent concentration of E. coli in stream water. Although the uncertainty of E. coli concentrations in streambed sediments and from wildlife probably affected the performance of the modified SWAT model, this study qualitatively confirmed the significance of modeling E. coli release from streambed and deposition for the SWAT microbial water quality simulations. Further developments should include modeling dynamics of bacteria populations within streambeds.     

New beach in a shallow estuarine lagoon: a model-based <Emphasis Type="Italic">E. coli</Emphasis> pollution risk assessment

A 3D hydrodynamic model has been applied to the Curonian Lagoon to study the pollution impact of E. coli on a new beach that might be opened in the lagoon. Through a field survey the E. coli inputs were measured and then used in the numerical model, and through laboratory experiments the decay rate of E. coli was established. The model has been calibrated and validated for the year 2015, and several scenarios have been studied, such as sewage system breakdown, severe weather conditions or high river loads. The model has then been run for a period of 12 years to obtain a robust statistics for the pollution on the planned beach. Results show that the decay rate of E. coli is between 0.55 days and 2.3 days and the modeled decay times are compatible with these numbers. The only scenario that would create a risk for the bathing waters of the beach is a breakdown of the sewage system on the Curonian Spit. In this case the hours (and days) over legally allowable bathing threshold were computed in order to estimate the number of days the beach could be closed. These results have been confirmed by the 12 year simulations. With an influence map analysis the two most critical sewage systems could be identified.     

Collembola gut passage shapes microbial communities in faecal pellets but not viability of dietary algal cells

Microarthropods are known as vectors for soil microorganisms, predominantly fungi. This laboratory study uses the widespread unicellular green algae Chlorella vulgaris as model to assess the role of Collembola in algal dispersal and to determine the effects of gut passage on propagation. Living algal cells were observed in 70 % of the faecal pellets of Folsomia candida, Heteromurus nitidus and Protaphorura fimata. Moreover, marker fatty acids for green algae, i.e. 16:2ω6,9 and 16:3ω3,6,9, were consistently detected in the pellets. Compared to the algal diet, the high content of methyl-branched total lipid fatty acid (TLFA) with hydroxyl substitution indicated microbial colonisation during gut passage. The TLFA profile of faeces revealed no species-specific differences but similar changes in microbial communities over the duration of feeding, indicating comparable indigenous bacteria and colonisation mechanisms during gut passage. In sum, faecal pellets of soil microarthropods such as Collembola can act as a vector for both dietary algae and specific gut-associated microorganisms, with the latter likely involved in resource degradation inside and outside the gut habitat.     

Verhalten von PAK im system boden/Pflanze

The results of lysimeter experiments conducted since 1991 dealing with the behavior of PAH in soil/plant systems demonstrate that the PAH pollution to cultivated plants may be caused by both atmospheric deposition and by the soil-to-plant transfer observed in contaminated sites. In the latter, a “direct contamination” of plant surfaces with PAH-loaded soil particles and the subsequent PAH turnover by desorption/adsorption processes is seen to dominate—at least for the most relevant PAHs toxic to humans, benzo(a)pyrene and dibenz(a,h)anthracene. Leafy vegetables growing close to the soil surface are therefore endangered most by a PAH contamination of the soil. The soil-to-plant transfer via “direct contamination” can be reduced to a high degree by covering the contaminated soil with different mulch materials. Systematic PAH transfer via root uptake could not generally be observed. From the reported results, a trigger value in the soil of 1 mg·kg^?1 for benzo(a)pyrene is proposed to make a judgement on PAH contaminated soils with regard to the soil-to-plant transfer pathways. Soils with excessive concentrations of benzo(a)pyrene demand special attention when considering the recommendations for the growth and consumption of cultivated vegetables. The “soil”as well as the “deposition pathways” must be integrated into a complete risk assessment of locations with food plant production, especially in urban areas.