A polychlorinated biphenyl-like chemical, a by-product of coal tar, was first discovered in 1865 and was synthesized in 1881. PCB compounds are a class of persistent, bioaccumulative and toxic organic pollutants. Their chemical structure consists of two benzene rings connected by a carbon-carbon bond. Based on the position and number of chlorine atoms present, there are 209 possible structures called congeners. In the year 1929, the Anniston Ordnance Company in Anniston, Alabama, U.S.A. began commercially producing PCBs in the form of Aroclors, which are a complex mixture that contain more than 80 congeners. Depending upon its composition, each Aroclor has a number, for example Aroclor 1242, Aroclor 1254, Aroclor 1260. The last 2 digits in these numbers indicate the percent by weight of chlorine in the mixture. However, Aroclor 1016 does not follow the same pattern as it contains 41% of chlorine by weight of the mixture.
The relationship between dissolved organic matter (DOM), commonly measured as dissolved organiccarbon (DOC), and mercury is very complex with studies showing differences in the association between DOM and mercury accumulation in fish (Gabriel et al. 2009). Dissolved organic matter can bind trace metals and affect the speciation, solubility, mobility and toxicity of mercury in the aquatic environment (Ravichandran 2004). Dissolved organic matter may enhance or retard methylation of mercury, serve as a transport mechanism for mercuryfrom terrestrial areas, or reduce the bioavaliability of inorganic and organicmercury species by binding to reaction sites (Ravichandran 2004). The enhanced mobility and transport of Hg-DOM complexes results in increased water column concentrations of mercury in otherwise pristine lakes and rivers (Ravichandran 2004). Dissolved organic matter also has the potential to enhance methylation of mercury by stimulating microbial growth (Ravichandran 2004). Dissolved organiccarbon may have a positive influence on fishmercury concentrations (McMurty et al. 1989; Wren et al. 1991; Rencz et al. 2003; Belger and Forsberg, 2006; Driscoll et al. 2007). However, a negative correlation between THg in several species of fish and lake water DOC (or water colour used as an indicator of DOC) has frequently been documented (Grieb et al. 1990; Snodgrass et al. 2000; Greenfield et al. 2001; Gabriel et al. 2009). Complexation of mercury with DOC may limit the amount of inorganic mercury available to methylating bacteria since DOC molecules are typically too large to cross the cell membranes of the bacteria (Ravichandran 2004). Thus, dissolved organiccarbon may prevent the biological uptake and methylation of ionic mercury within a waterbody (Munthe et al. 2007). Moreover, DOC is suspected to enhance photoreduction of Hg 2+ to Hg 0 further reducing the bioavailability within an aquatic environment (O'Driscoll et al. 2003; Hall et al. 2008; Gabriel et al. 2009). Thus, contradictory results may be due to multiple ecological factors that complicate the net effect of lake water DOC concentrations on mercury concentrations in fish.
The FAO/WHO report (FAO/WHO, 2011) gave conclusions on possible risks and benefits of fish consumption on cardiovascular disease based on 19 prospective cohort studies and five clinical trials. They concluded that there was strong evidence that consumption of long-chain n-3 fatty acids from either fish or fish oil supplements lowers the risk of cardiovascular disease, especially death from coronary heart disease and sudden cardiac death. The dose- response relationship did not appear to be linear. A pooled analysis of 20 large studies in humans was found to support this non-linear effect for death from coronary disease, with a 36% risk reduction up to 250 mg EPA+DHA per day and then little additional lowering of risk at higher doses. Results were very similar when restricted to prospective cohort studies of seafood consumption in generally healthy (primary prevention) populations. Thus, overall benefits of fish or fish oil consumption for death from coronary heart disease appeared very similar in prospective cohort studies of fish consumption in generally healthy people (primary prevention) compared with controlled trials of fish oil in individuals with established heart disease (secondary prevention). Population groups included in these trials and cohorts which included studies in the USA, Europe, Asia and Australia varied, suggesting that coronary heart disease benefits are applicable across a wide range of countries and background diets. The Expert Consultation concluded that there is convincing evidence from extensive
anabolic reactions, particularly fatty acid synthesis (14 NADPH per C16:0 FA, 62 NADPH per C16:0 FA if acetyl-CoA production included) . The major alternative pathway for NADPH production is the last stage (PSI) of the photosynthetic linear electron transport, consequently a degradation of the photosynthetic machinery is likely to lead to a simultaneous upregulation of the OPPP pathway, particularly if NADPH demand is maintained through lipid synthesis. The GLD2 gene (Cre08.g378150), encodes for the enzyme glucose-6-phosphate dehy- drogenase (Fig. 1). This enzyme is involved in the ﬁrst step in the PP pathway, the conversion of glucose-6-phosphate into 6-phosphogluco- nolactonase (producing 1 NADPH, Fig. 1). Goodenough et al.  de- monstrated that nitrogen stress induced an upregulation of GLD2 and downstream OPPP genes in mixotrophic C. reinhardtii under continuous light (similar to M-24-NF); however the impact of di ﬀ erent light and carbon regimes on the activity of glucose-6-phosphate breakdown through the OPPP is not known. As expected, GLD2 expression in M-24- NF was upregulated rapidly, increasing 3 fold after 2 h in NF medium (LOG-2 h, p > 0.05) (Fig. 4D). Expression remained stable, with the exception of a spike at 24 h (1.8 fold increase between 14 and 24 h, p < 0.001). The expression trend was very similar in M-12-NF, in- creasing 3.3 fold after 2 h (LOG-2 h, p < 0.01) and remaining stable, with the exception of a small drop (1.64 fold, p < 0.05) after 36 h. The gene GLD2 was also upregulated in autotrophic treatments although at a more gradual rate, increasing 3.1 fold (p < 0.01) over 48 h for A-24- NF. However, the peak expression was 3.2 fold lower than M-24-NF. Expression of GLD2 in A-12-NF increased at a similar rate to A-24-NF, however expression dropped at 24 h (3.5 fold drop, p < 0.05) and 48 h (5.9 fold drop, p < 0.05), and is assumed to be downregulated (or post 14 h) during the dark period.
Wildfire emissions are composed primarily of car- bon dioxide, many organic species and black carbon (Yokelson et al., 2007); their shares are dependent on the meteorological conditions, type of vegetation, humidity, and topography of the terrain, among oth- er factors. Organic compounds emitted by fires are reactive species that play a role in the formation of ozone and secondary organic aerosols in addition to many other organic compounds, such as benzene and toluene, degradation products from biopolymers, n-alkanes, n-alkenes, n-alkanoic acids, n-alkanols, monosaccharide derivatives from cellulose, steroids and terpenoid biomarkers, and polycyclic aromatic hydrocarbons (primarily retene) (Yokelson et al., 2007; Evtyugina et al., 2013), which are known to be toxic to human health. Excluding agricultural burning, recent estimates suggest that wildfires account for approxi- mately half of the global BC and CO emissions and two-thirds of OC emissions (UNEP and WMO, 2011). However, no global black carbon emission inventory is available from the United Nations Framework Con- vention on Climate Change (UNFCCC).
The aim of the study was to describe the distribution of total mercury in the tissues of fish originating from important Czech fishing locations and to determine the level of methylmercury as a percentage of total mercury (Hg speciation). At six important fishing locations a total of 144 fishes of 13 species were caught and analysed. Samples of muscle, liver, gonads and scales were analysed for total mercury and in the case of muscles for methylmercury concentrations. Total mercury was determined by AAS using an AMA 254 analyser, and methylmercury determination was performed by GC/ECD using a GC-2010A chromatograph. Total mercury concentrations in muscle and other tissues of all the fishfrom all fishing locations were below 0.5 mg/kg, with the exception of 6 asps (Aspius aspius). A significant (P < 0.05) correlation was found between the total mercury concentrations in scales and other tissues. Methylmercury made up about 46–100% of total mercury in muscle. The overall results confirmed the good hygienic quality of fishfrom important Czech fishing locations.
It must, however, be emphasized that there are many uncertainties in these estimates. They are based on very few studies, and the results of these studies span a large range of impacts. The sites studied may also not be a representa- tive sample of the landscape. For instance the data is largely from sites without wetlands. And even if the data was a fair representation of the landscape, there will be local variations in the forest area impacted, and the sensitivity of the areas. There are also likely to be regional dif- ferences, both in operational methodologies, and the susceptibility of the landscape to for- est impact – for instance between shallow soils with large rainfall in the southwest of Sweden, and regions with deeper soils and less rainfall in Finland or central Canada. This variable sensi- tivity is exemplified by the difference between the Ontario study (Table 4) where a clear fel- ling gave little change in concentrations, to the Gårdsjön situation where a single logging road led to a manifold increase in run-off concentra- tions of MeHg.
Several studies on Hg elimination in freshwater and marine fish species (Ruohtula and Miettinen, 1975; Wang and Wong, 2003) reported a pattern of biphasic elimination, where there was a rapid loss of chemical immediately after dosing, followed by a slower loss process. Biphasic elimination kinetics was not observed in our study, which might be a result of the differences in the dosing method between this study and the earlier cited studies. Lags associated with the inter-tissue transport kinetics post assimilation often result in higher blood concentrations of the chemical relative to other tissues following initial chemical exposure (Gobas et al. 1988). Given the role of blood as a central compartment and its stronger association with chemical elimination, an elevated blood concentration favors a higher initial elimination of chemicals (Barron et al. 1990). In this study, fish were exposed to a naturally contaminated diet for several weeks prior to initiation of elimination, whereas fish in other studies were typically given a single oral dose, an intra muscular injection or a short term (from several hours to days) aqueous exposure. The dosing methodology of our study is more representative of natural exposure and uptake dynamics given that the Hg was ingested in a form (i.e. protein- associated) more consistent with Hg exposures taking place in aquatic ecosystems.
Adsorption is a surface phenomenon in which adsorbate molecules, atoms or ions attract to unsaturated positions on the surface of adsorbent because of unbalanced molecular forces. After adsorption reach equilibrium the concentration of adsorbate particles on the solid surface of adsorbent would be higher than their concentration in bulk solution. Adsorption could be a chemical or physical process or a combination of both. Van der Waals forces are responsible for physisorption while chemisorption occurs through redistribution of electrons between adsorbent and adsorbate and the following strong chemical bond. Due to the nature of physisorption, it is a weak alterable and not site- specific process. However the main characteristic of chemisorption is forming a unimolecular thickness of the adsorbed phase caused from strong irreversible and site specific chemical bonds , –. The adsorption process on porous adsorbent is generally defined with three main stages. First, the adsorbate is transported from bulk solution to the external surface of the adsorbent (film-diffusion or external-diffusion). Next, the adsorbate transport within the pores of the adsorbent (internal diffusion). In this step that is the rate limiting, a small amount of adsorption occurs on the external surface which is called particle diffusion. At final step the adsorbate is adsorbed on the inner surface of the adsorbent pores and capillary spaces. This is the equilibrium step. The interaction between the adsorbate, matrix and surface of adsorbent have effected on these steps and the resulting metal adsorption. Parameters that could influence on adsorption are included pH, temperature and presence of competitive ions of the adsorption matrix; chemical and physical properties of adsorbate such as ionic radius and solubility; and adsorbent surface chemistry and characteristics , –.
For isotherms in ultrapure water, adsorbent doses between 10 and 7500 mg/L were utilized. Adsorbents were placed into brown glass bottles that were subsequently filled to the neck with the amended ultrapure water. Micropollutant stock solutions were added with a constant rate syringe (CR-700, Hamilton, Reno, NV) to yield an initial concentration of about 1000 µg/L. Once the micropollutant was added to a bottle, it was topped off immediately with ultrapure water to create headspace-free conditions and capped using PTFE-faced silicon septa and open-top closures. A mixing time of 2 weeks in a rotary tumbler was sufficient to reach adsorption equilibrium. Upon equilibration, adsorbents were separated from the liquid by sedimentation (ACFs) or filtration through 0.45 µm filters (pulverized GACs). Remaining liquid-phase TCE and MTBE concentrations were measured by purge and trap concentrator followed by gas chromatographic (Shimadzu 14a, Columbia, MD) and flame ionization detector (FID). The micropollutant concentrations were quantified using external standards.
The goal of this work was the valorization of the sawdust from Triplochyton Scleroxylon wood as a biosorbing agent for the removal of Hg(II) ions from the aqueous solution. The adsorption capacity of sawdust was increased by an alkaline treatment and the maximum NaOH uptake was observed for a temperature of 30 °C. The experimental results show that base treated sawdust yielded a higher biosorption capacity for Hg(II) than unmodified sawdust. The adsorption process is dependent on numerous factors such as the contacting time, the biosorbent dose, the solution pH, the Hg(II) initial concentration, the ionic strength and the metal co-cations. In particular, mercury(II) adsorption onto unmodified and modified sawdust was fast during the first 20 min and thereafter it slowly reached a pseudo-equilibrium in 60 and 30 min for unmodified and modified sawdust, respectively. The biosorption kinetic followed the pseudo-second order model, which indicates that mercury removal might be a chemisorptions process. For all the biosorbent, biosorption is maximal at pH 7 and the Hg(II) uptake are 1.80 and 1.91 mg g -1 at neutral pH during 60 min using unmodified and modified sawdust, respectively. The biosorption isotherms were better fitted by Langmuir model. The alkaline treatment of sawdust improves the predicted maximum Hg(II) adsorption capacity from 5.32 to 6 mg g -1 at pH 7. Both ionic strength of solution and metal co-cations decrease mercury(II) uptake by modified sawdust, with the order Na + > Ca 2+ > K + . Mercury(II) ions adsorbed on modified sawdust were better desorbed by EDTA than HCl and HNO 3 . The maximum desorption ratio of 48 % is achieved within 60 min using
Levels and trends of total mercury (THg) and methylmercury (MeHg) compounds in bream (Abramis brama) from different European sites were compared. Bream were collected between 2007 and 2013 in the estuaries of the rivers Scheldt (Netherlands), Rhône (France), Göta älv (Sweden), Tees (United Kingdom), and Mersey (UK), and in Lake Belau (Germany). A direct mercury analyzer was used to deter- mine THg concentrations while MeHg was measured by gas chromatography/inductively coupled plasma-mass spectrometry applying stable isotope dilution. THg and MeHg in annual pool samples of bream ranged between 15.9 and 251 l g kg 1 wet weight (ww) with lowest concentrations found at the reference site Lake Belau and highest in samples from the river Rhône. The EU environmental quality standard (EQS) of 20 l g kg 1 ww was exceeded at all sites and in all years except at Lake Belau in 2012. Signiﬁcantly decreasing trends over time were observed only in bream from the Rhône, while THg increased in bream from the Western Scheldt. The MeHg fractions of THg were always >80% and a signif- icant difference between sites was detected only in one case (Rhône vs. Lake Belau).
Figure 3. Sediment-inferred lake-water total organiccarbon concentrations (TOC; mg·L -1 ) using the Northern lakes TOC model (open circles) for the 1982 sediment varve from Nylandssjön, northern Sweden, and the respective relative C loss in the samples (area plot) 41 based on the original concentration in the 1983 core (16.1 wt% C), which demonstrates the impact of diagenesis on the sediment organic matter composition over 27 years. The horizontal black line indicates average inferred lake-water TOC concentration across all
Results: An initial rapid uptake of benzene was observed and became almost constant after 40 minutes of contact. Kinetic data was analyzed using pseudo first order, pseudo second order, and Elovich equations. Kinetic data was well fitted to pseudo-second order models (R 2 = 0.98), indicating chemisorption. Results from intraparticle diffusion and Boyed models indicate that particle diffusion is the most probable operating mechanism and does not control the kinetics of benzene sorption. A comparative study on the benzene adsorption revealed that the rice husk carbon (RHC) had better benzene adsorption capacity (365 mg/g) as compared to other adsorbents.
Abstract. Even though human induced eutrophication has severely impacted temperate lake ecosystems over the last centuries, the effects on total organiccarbon (TOC) burial and mineralization are not well understood. We study these effects based on sedimentary records from the last 180 years in five Swiss lakes that differ in trophic state. We compare changes in TOC content and modeled TOC accumulation rates through time to historical data on algae blooms, water column anoxia, wastewater treatment, artificial lake ventilation, and water column phosphorus (P) concentrations. We furthermore investigate the effects 20
ABSTRACT: With the growth and development of chemical plants, the amount of mercury released in wastewater has increased. Mercury in wastewater contains harmful compounds which are hazardous to the human health and living organisms. Therefore, its removal from wastewater is significant. There are various techniques or methods available for removing mercuryfromaqueous solutions. This study focused upon the removal of mercuryfromaqueous solution with commercial activated carbon and activated carbonfrom sugarcane bagasse. Activated carbon produced from sugarcane bagasse was used as adsorbent. This adsorbent was used to remove mercuryfromaqueous solution. For this purpose, first, the optimal mercury solution pH for mercury removal was obtained. Effective parameters such as contact time, initial concentration of mercury, adsorbent dose and agitation speed were investigated. The mercury adsorption was increased when the mass of activated carbon was increased. Increasing the initial mercury concentration leads to decrease in mercury adsorption efficiency. The results of experiments indicated that the speed of the stirrer was not considered to be an effective factor in the mercury adsorption. Experiments were also carried out on a commercial activated carbon. Adsorption results obtained for sugarcane bagasse activated carbon were compared with commercial activated carbon. The adsorption efficiency was increased as the contact time was increased. Finally, the experiment was carried out on water samples released from South Pars platforms. In addition to the mercury removal, other heavy metals removal such as lead and cadmium were also carried out.
Soil contamination with heavy metals will lead to losses in agricultural yield and hazardous health effects as they enter into the food chain (Schickler and Caspi 1999). the effects of heavy metals on cellular system have received a great deal of at- tention due to the increasing exposure of living organisms to these metals in the environment. Mercury (Hg) is one of the major pollutants in soils because of the annual import of toxic Hg into the agricultural lands (Patra and Sharma 2000). in addition, Hg is a highly toxic non-essential element and its dispersion in the environment is considered to be a global problem for its persistent character. Compared with Cd, Co, Cu, Pb, and Zn, Hg has the greatest inhibitory effects on seed germina- tion, root elongation, and hypocotyl and coleoptile growth in wheat (Munzuroglu and Geckil 2006). it was found that Hg released to soils remains mainly in the solid phase through adsorption onto sulfides, clay particles and organic matters. the predominant form of Hg in agricultural soils is the ionic form (Hg 2+ ) (Han et al. 2006).
At her annual physical examination, a 28-year-old uni- versity student says that she is to be married next year, when she wants to go off the pill and try to conceive. She lives at home with her parents, immigrants to Canada from Hong Kong. She eats a tuna submarine sandwich for lunch at least 3 days a week at school and has sushi once a week. She also eats fish with her fami- ly approximately 3 times a week. She has read an article suggesting that she might be eating too much fish. How would you counsel her about fish eating and pregnancy? Fish is a healthy dietary choice for women in their reproductive years, with health benefits for their future children, but there is concern that mercury in some fish species could harm a developing fetus. Preconception and prenatal visits offer effective opportunities for family physicians to improve maternal and child health. 1 It is a
concentrations of this contaminant with increasing trophic position (Bowles et al., 2001). Hence, we broadly partitioned the fish into three feeding guilds – primary, secondary, and tertiary consumers – based on published dietary data on Lake Kinneret. Fish THg concentrations increased significantly with increasing trophic guild. The THg concentrations of tertiary consumers, for which fish are an important dietary component, were approximately 4-fold higher than for secondary consumers and 22-fold higher than for primary consumers. The mercury concentration in St. Peter’s fish, which feed primarily on the algae Peridinium but also on some zooplankton, was 4-fold lower than lavnun, which feed on zooplankton and are one trophic level higher (Zohary et al., 1994). Large-scaled barbel and catfish, the two tertiary consumers examined in this study, ingest a wide range of plants and animals (>50 species) in Lake Kinneret, however, fish is the most important dietary component of both species, and lavnun is the main consumed fish (Spataru and Gophen, 1985b; Spataru et al., 1987). Mercury concentrations in barbel and catfish were ~3-fold and 8-fold higher, respectively, than in lavnun. The mercury biomagnification between prey and predatory fish generally ranges 3-10x, suggesting that trophic transfer of MeHg in Lake Kinneret is similar to tropical and temperate freshwater ecosystems (Bowles et al., 2001; Wiener et al., 2003).