In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 μg L−1 for 6–7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly – approximately 1315 (±442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 ± 1.55) than from periphyton grown in Jan 2009 (0.85 ± 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers. Periphyton is a major source of Cd bioaccumulation in a grazing mayfly.

The attenuation and fate of erythromycin-resistance-methylase (erm) and extended-spectrum beta-lactamse (bla) genes were quantified over time in aquatic systems by adding 20-L swine waste to 11,300-L outdoor mesocosms that simulated receiving water conditions below intensive agricultural operations. The units were prepared with two different light-exposure scenarios and included artificial substrates to assess gene movement into biofilms. Of eleven genes tested, only erm(B), erm(F), blaSHV and blaTEM were found in sufficient quantity for monitoring. The genes disappeared rapidly from the water column and first-order water-column disappearance coefficients were calculated. However, detected gene levels became elevated in the biofilms within 2 days, but then disappeared over time. Differences were observed between sunlight and dark treatments and among individual genes, suggesting that ecological and gene-specific factors play roles in the fate of these genes after release into the environment. Ultimately, this information will aid in generating better predictive models for gene fate.

The Northern Patagonian Andean range shared by Chile and Argentina has numerous glacial oligotrophic lakes protected in a series of National Parks. Recent baseline surveys indicated that concentrations in muscle and liver tissues from various fish species from across Nahuel Huapi and Los Alerces National Parks in Argentina were comparable or higher than similar fish species from other parts of the world. As a result, Lake Moreno, in Nahuel Huapi National Park, was chosen to investigate multiple element sinks, trends, and transfer in a representative Patagonia aquatic food web. The metals and metalloids Ag, As, Ba, Br, Cs, Co, Cr, Fe, Hg, K, Na, Rb, Se, and Zn were analyzed in three size plankton fractions, submerged macrophytes, biofilm, insect larvae, amphipods, decapods, gastropods (snails), annelids (earthworms), and forage fish. Except for nanoplankton (10-53 μm; small-celled algae, rotifers) and microplankton (53-200 μm; larger algae, ciliates, zooplankton nauplii), which share elemental compositional similarities, each taxon category had its own distinctive compositional pattern, revealed by principal component analysis. Nano- and microplankton tend to be relatively elevated in some metals, including As, Co, Cr, Fe, Hg, Zn, and Rb, followed by biofilm. Shredder-scrapper Trichoptera (caddisflies) have higher concentration of most of the studied elements than other insect larvae taxa, especially carnivorous Odonata (Anisoptera, dragonflies), which were associated with lower elemental contents. Those trends point to an overall tendency for biodiminishing element concentrations with trophic level in the benthos of Lake Moreno.

Background, aim, and scope Due to the active production and transport of crude oil in the Arabian Gulf region, the Arabian Gulf coasts are routinely polluted with oil. Therefore, such coasts have been subject of studies aiming at assessing the roles of indigenous microbial consortia in cleaning these environments. In the present study, epilithic microbial communities along Kuwait coasts were studied for their oil degradation potential. Materials and methods Gravel particles coated with deep green biofilms were collected from four coastal sites in autumn, winter, and spring. Phototrophs in these consortia were determined in terms of their chlorophyll a contents and identified by their morphological characteristics. Total bacteria were counted microscopically and cultivable bacteria by the dilution plating method on nutrient agar as well as on inorganic medium containing oil as a sole source of carbon and energy. The bacterial community structures were also characterized and compared by denaturing gradient gel electrophoresis (DGGE). Results Epilithic biomass samples from the four sites in the three seasons were rich in diatoms and picocyanobacteria as well as total bacteria. Direct counting gave bacterial numbers per square centimeter gravel surface of 2 to 6 × 10⁷ cells depending on the sampling site and season. Cultivable bacterial numbers on nutrient agar and crude oil as a sole source of carbon were 3 × 10³ to 8 × 10⁴ and 1 × 10³ to 7 × 10³ cells/cm² gravel surface, respectively. The DGGE profiles of epilithon biomass samples revealed major 16S rDNA bands that matched bands of pure oil-utilizing bacterial isolates. Discussion The microbial communities showed a degree of consistency in all sites and seasons. Conclusions The microbial consortia coating gravel particles are potentially suitable tools for self-cleaning of oily Gulf coasts. They are rich in oil-utilizing bacteria whose activities are probably enhanced by oxygen produced by the phototrophic partners in the consortia. Recommendations and perspectives The combination of conventional microbiological analysis with molecular approaches gives an enhanced idea about natural microbial communities especially those with environmental application potential.

Concept and purpose Virtually all water treatment facilities worldwide generate an enormous amount of water treatment residual (WTR) solids for which environmentally friendly end-use options are continually being sought as opposed to their landfilling. Aluminium-based WTR (Al-WTR) can offer huge benefits particularly for phosphorus (P) removal and biofilm attachment when used as media in engineered wetlands. However, potential environmental risks that may arise from the leaching out of its constituents must be properly evaluated before such reuse can be assured. This paper presents results of an assessment carried out to monitor and examine the leachability and leaching patterns of the constituents of an Al-WTR used as media in laboratory-scale engineered wetland systems. Main features, materials and methods Al-WTR was used as media in four different configurations of laboratory-scale engineered wetland systems treating agricultural wastewater. Selected metal levels were determined in the Al-WTR prior to being used while levels of total and dissolved concentration for the metals were monitored in the influent and effluent samples. The increase or decrease of these metals in the used Al-WTR and their potential for leaching were determined. Leached metal levels in the effluents were compared with relevant environmental quality standards to ascertain if they pose considerable risks. Results Aluminium, arsenic, iron, lead and manganese were leached into the treated effluent, but aluminium exhibited the least leaching potential relative to its initial content in the fresh Al-WTR. Levels of P increased from 0.13 mg-P/g (fresh Al-WTR) to 33.9-40.6 mg-P/g (used Al-WTR). Dissolved levels of lead and arsenic (except on one instance) were below the prescribed limits for discharge. However, total and dissolved levels of aluminium were in most cases above the prescribed limits for discharge, especially at the beginning of the experiments. Conclusions, recommendations and perspectives Overall, the study indicates that leaching is observed when Al-WTR is beneficially reused for enhanced P removal in engineered wetlands. In particular, levels of aluminium in the treated effluent beyond the prescribed limits of 0.2 mg/l were observed. However, since the results obtained indicate that aluminium leached is mostly associated with solids, a post-treatment unit which can further reduce the level of aluminium in the treated effluent by filtering out the solids could serve to mitigate this. In addition, plants used in such wetland systems can uptake metals and this can also be a potential solution to ameliorating such metal releases. Periodic monitoring is thus advised. Notwithstanding, the use of Al-WTR as a media in engineered wetlands can serve to greatly enhance the removal of P from wastewaters and also serve as support material for biofilm attachment.

Background, aim, and scope Solid surfaces in contact with water have been found to be biofouled due to the attachment of various organisms. For better understanding of the biofilm formation, the important initial stage of bacterial attachment was investigated with Pseudomonas aeruginosa PAO1 as a model microorganism. Effects of the biosurfactant rhamnolipids and the shear conditions were particularly examined. Materials and methods A highly reproducible procedure was employed. The procedure involved monitoring and counting the number of attached cells on glass walls of the flow chambers, through which a PAO1 suspension was circulated and, subsequently, a saline solution was passed for washing. The experiments were made under different circulation rates (exerting different shear on the bacteria) and rhamnolipid concentrations. Results and discussions Reproducibility of the procedure was confirmed. The velocity profiles near the flow chamber wall were determined. Rhamnolipids, even at a very low concentration of 13 mg/l, were found to deter the bacterial attachment substantially. Prewashing the cells with a 100 mg/l rhamnolipid solution, however, did not affect the attachment significantly. As for the effect of shear, the PAO1 attachment showed an increasing-then-decreasing trend in the range investigated, i.e., 1.0 to 26 mN/m² shear stresses at the chamber wall. The diffusion-limited transport of cells to the chamber wall might have contributed to, but could not fully explain, the increasing attachment observed in the very low shear range (up to 3.5-5.0 mN/m²). Conclusions As compared to static systems, the flow chamber systems significantly improved the reproducibility of initial attachment results. Flow chamber systems were more suitable for experimental investigations of bacterial attachment to surfaces. Rhamnolipids were found to be potent antifoulants for PAO1 attachment on glass. The initial cell attachment increased with increasing shear at the very low shear range (up to 3.5-5.0 mN/m²), but the attachment could be minimized with further increase of the shear.