High-resolution insight into the competitive adsorption of heavy metals on natural sediment by site energy distribution.

Investigating competitive adsorption on river/lake sediments is valuable for understanding the fate and transport of heavy metals. Most studies have studied the adsorption isotherms of competitive heavy metals, which mainly comparing the adsorption information on the same concentration. However, intrinsically, the concentration of each heavy metal on competitive adsorption sites is different, while the adsorption energy is identical. Thus, this paper introduced the site energy distribution theory to increase insight into the competitive adsorption of heavy metals (Cu, Cd and Zn). The site energy distributions of each metal with and without other coexisting heavy metals were obtained. It illustrated that site energy distributions provide much more information than adsorption isotherms through screening of the full energy range. The results showed the superior heavy metal in each site energy area and the influence of competitive metals on the site energy distribution of target heavy metal. Site energy distributions can further help in determining the competitive sites and ratios of coexisting metals. In particular, in the high-energy area, which has great environmental significance, the ratios of heavy metals in the competitive adsorption sites obtained for various competitive systems were as follows: slightly more than 3:1 (Cu-Cd), slightly less than 3:1 (Cu-Zn), slightly more than 1:1 (Cd-Zn), and nearly 7:2:2 (Cu-Cd-Zn). The results from this study are helpful to deeply understand competitive adsorption of heavy metals (Cu, Cd, Zn) on sediment. Therefore, this study was effective in presenting a general pattern for future reference in competitive adsorption studies on sediments.

A promising approach to enhance microalgae productivity by exogenous supply of vitamins.

In order to reduce the consumption of traditional fossil fuels and their impact on the environment, strategies to mitigate greenhouse gas emissions especially carbon dioxide needs exploration. Microalgae-based biofuels can be the best-fit plant based feed-stocks for diminishing a majority of the Universe's energy problems. Interestingly, the eukaryotic microalgae aid in fixation of almost 50% of the global carbon in the environment. Thus, determination of parameters that will enhance microalgal growth and productivity is crucial, if they are to be used as future renewable energy sources. A large percentage of phytoplankton species are auxotroph for one or more vitamins. These species, in turn, are also dependent upon the vitamin biosynthetic pathways for processing of these vitamins. The present study serves as a base to discuss the prevalence of vitamin auxotrophy in microalgae and the methods of its acquirement from external sources such as heterotrophic bacteria. The next section of the paper sheds light on possible species-specific symbiotic interactions among microalgae and bacteria. Lastly is the discussion on how heterotrophic bacteria can act as a vitamin prototroph for an explicit microalgal vitamin auxotroph. The overall focus is placed upon harnessing these symbiotic interactions with intentions to obtain enhancements in microalgal biomass, lipid productivity, and flocculation rates. Moreover, the growth and distribution of a microalgal cell that thrives on a specific vitamin is perhaps met by growing it with the bacterial communities that nourish it. Thus, possibly by ecologically engineering a potential species-specific microalgal-bacterial consortium, it could tremendously contribute to the acceleration of photosynthetic activity, microalgal productivity, exchange of primary metabolites and other biogeochemical nutrients within the mini ecosystem.

Spatial distribution, ecological risk assessment, and potential sources of heavy metal(loid)s in surface sediments from the Huai River within the Bengbu section, China.

The Huai River is one of the major drinking water resources in Bengbu City of China's eastern Anhui Province. The study focused on extracting information for spatial distributions of heavy metal(loid)s (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) based on the contents of pollutants in 20 surface sediments. Geoaccumulation index and Hakanson potential ecological index were used to calculate the ecological risk of sediment environment in this paper. The I geo results indicated that the sediments were moderately contaminated by Hg and Pb. The potential ecological risk sequence of the metals was Hg > Cd > Pb > Cu > Ni > Cr > Zn > As. Among the metal(loid)s, Hg was the main source of pollution that contributed ∼76% towards the potential ecological risk, followed by Cd. Finally, multivariate statistical analysis methods were conducted to identify the potential causes of pollution and provide basis for environment treatment in Bengbu Reach. The results depicted that Pb may be mainly derived from the traffic emission and manufacturing industry, while Hg may be originated from agricultural emissions.

Survival & detection of the faecal indicator bacterium Enterococcus faecalis in water stored in traditional vessels.

BACKGROUND & OBJECTIVE: Enterococci are used as indicators of faecal pollution and are typically detected using agar-based growth media incubated under standard aerobic conditions. However, such conditions may not be fully effective in enumerating injured bacteria, due to their sensitivity to reactive oxygen species (ROS) under aerobic conditions. Investigations were carried out to assess the extent of sub-lethal damage and ROS-sensitivity on different strains of Enterococcus faecalis in water stored in traditional brass and earthern vessels by enumerating the bacteria under standard aerobic conditions and under conditions designed to neutralize the effect of ROS. METHODS: Pure cultures of E. faecalis were maintained for up to 48 h in brass and earthern vessels and enumerated on various selective and non-selective media either under (i) standard aerobic conditions, (ii) aerobic conditions in a growth medium supplemented with the peroxide scavenger sodium pyruvate, (iii) anaerobic conditions using unsupplemented medium; and (iv) anaerobic conditions in a growth medium supplemented with sodium pyruvate, the latter being regarded as ROS-neutralized conditions. RESULTS: Counts of E. faecalis decreased substantially after storage for 12 h in water kept in the brass vessel but not in the earthern vessel. However, the decrease in counts depended upon the growth medium and the conditions used for enumeration, with a non-selective medium giving the highest count under ROS-neutralized conditions. While the counts obtained on various selective media were also enhanced under ROS-neutralized conditions, they remained lower than those of the non-selective medium. INTERPRETATION & CONCLUSION: Our study showed that growth conditions where reactive oxygen species are neutralized, were effective in enhancing the colony count of stressed E. faecalis, irrespective of the type of medium used for enumeration.

Inactivation of Escherichia coli and coliform bacteria in traditional brass and earthernware water storage vessels.

The detection and enumeration of indicator bacteria such as Escherichia coli is used to assess the extent of faecal contamination of drinking water. On the basis of this approach, the effectiveness of storing water contaminated with faecal indicator bacteria in brass or earthern vessels (mutkas) of the type used in rural India have been investigated. Suspensions of bacteria in sterile distilled water were maintained for up to 48 h in each vessel and enumerated by surface plate counts on nutrient agar (non-selective) and several selective coliform media at 37 degrees C either under standard aerobic conditions, or under conditions designed to neutralise reactive oxygen species (ROS), e.g. using an anaerobic cabinet to prepare plates of pre-reduced growth medium or by inclusion of sodium pyruvate in the growth medium, with incubation of aerobically-prepared plates in an anaerobic jar. The counts obtained for E. coli decreased on short-term storage in a brass mutka; counts for selective media were lower than for equivalent counts for non-selective medium, with ROS-neutralised conditions giving consistently higher counts than aerobic incubation. However, after 48 h, no bacteria were cultivable under any conditions. Similar results were obtained using water from environmental sources in the Panjab, and from rural households where brass and earthern mutkas are used for storage of drinking water, with enumeration on selective coliform media (presumptive total coliforms). In all cases results indicated that, while storage of water in a brass mutka can inactivate E. coli and coliforms over a 48 h period, standard aerobic plate counting using selective media may not be fully effective in enumerating sub-lethally damaged bacteria.