Formation and availability of methylmercury in mercury-contaminated sediment: effects of activated carbon and biochar amendments

Purpose As the formation of toxic and bioaccumulative methylmercury (MeHg) in Hg-contaminated sediments is of great concern worldwide, suitable remediation options are needed. Activated carbon (AC) amendment is a contested alternative due to uncertainties surrounding sorption efficiency and its potential role in aiding MeHg formation. The purpose of this study was therefore to demonstrate AC performance under favourable conditions for Hg-methylation and to further understand the role AC plays in the methylation process. Materials and methods Mercury-contaminated sediment (57.1 mg kg−1) was sampled from the Gunneklev fjord, a site known as the most heavily contaminated fjord in Norway. In a laboratory experiment, lignite AC (A-AC, 5%) or activated biochar (A-BC, 5%) along with dried algae biomass, serving as an excess source of easily degradable organic matter (OM) and sulphate, were added to sediment samples that were kept anoxic and dark over a period of 12 months. Results and discussion The amount of MeHg in sediment and porewater of the amended samples were measured at 0, 1, 3, 6, and 12 months and compared to an unamended control. A net increase of MeHg in the sediment was observed in both control and amended samples, but contrary to expectations, sediment MeHg was 5 and 3 times higher in the A-AC and A-BC treatments, respectively, relative to the control after 12 months. As the stimulation of Hg-methylation could not be attributed to the sorbents supplying more available OM or sulphate for dissimilatory sulphate reduction, it is speculated that the sorbents rather aid this process through shuttling of electrons between the substrates involved. Meanwhile, the A-AC and A-BC amendments strongly reduced the available MeHg-concentration in porewater (by 87% for A-AC and by 93% for A-BC after 12 months), confirming that AC sorbents can be used to effectively limit the transport of MeHg from sediments. Conclusion When considering remediation of OM-rich Hg-contaminated sediments with AC, caution is thus warranted, as the overall effect of reducing MeHg-transport out of the sediment could partly be offset by an increased fraction of MeHg in the sediment. Thin-layer capping with AC might therefore be preferable to complete mixing of AC and sediment.

Preliminary Investigation of Microplastics in Sediments from Industrial Manufacturing Waste Sources

Microplastics (particles with a size of less than 5 mm) are a rising environmental problem. Microplastics can disseminate in the air and accumulate in sediments as well as in microorganisms and humans, due to their small size. Sediment is considered to be the major repository of microplastics, particularly those of the PE type. Microplastics in massive amounts accumulated in sediments, perhaps as a result of point sources or diffuse contamination. Microplastic contamination can spread from industrial production facilities, urban areas, agricultural areas, or the air. The current study was carried out to explore the occurrence of MPs in sediments at discharge sources by evaluating 27 sediment samples taken from 9 distinct waste sources from industrial activity locations to determine the amount of microplastic contamination in sediments at discharge sources. Microplastics with relatively high density were found in all sediment samples in this research, ranging from 2,900 to 238,200 particles/kg dw. The most prevalent microplastics detected in sediment samples at these sites were fibers and fragments, accounting for 59-94% and 6-41%, respectively. Fiber microplastics ranged in size from 1000 to 9,000 µm, whereas fragment microplastics ranged from 200,000 to 2,100,000 µm2. Microplastics with < 1000 µm and 1000-2000 µm sizes accounted for a significant portion of the total, reaching 21.05-37.84% and 39.74-61.17%, respectively. The hue of microplastic particles in sediment samples obtained was highly varied.

Spatial and temporal analysis of the risks posed by metal contamination in coastal and marine sediments of Bahrain

Nine metals including Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were analysed from sediment samples collected from 29 stations since 2007 from Bahraini waters. Within this study, it was investigated whether concentrations of these determinants are at concentrations above internationally established Assessment Criteria (AC). The majority of sites were considered not to pose a toxicological risk in terms of metal contamination. Where breaches occurred, they were mainly from historic samples related to Cr, Cu and Ni contamination. A trend assessment revealed that out of 59 significant trends, 36 were downwards and 23 upwards, indicating that some determinants like Al, Zn and Ni are improving strongly across some sites, whilst areas associated with industrial activity still see some increasing trends for Al, Cd, Pb and Zn.

Use of Stress Signals of Their Attached Bacteria to Monitor Sympagic Algae Preservation in Canadian Arctic Sediments

Based on the strong aggregation of sympagic (ice-associated) algae and the high mortality or inactivity of bacteria attached to them, it was previously hypothesized that sympagic algae should be significant contributors to the export of carbon to Arctic sediments. In the present work, the lipid content of 30 sediment samples collected in the Canadian Arctic was investigated to test this hypothesis. The detection of high proportions of trans vaccenic fatty acid (resulting from cis-trans isomerase (CTI) activity of bacteria under hypersaline conditions) and 10S-hydroxyhexadec-8(trans)-enoic acid (resulting from 10S-DOX bacterial detoxification activity in the presence of deleterious free palmitoleic acid) confirmed: (i) the strong contribution of sympagic material to some Arctic sediments, and (ii) the impaired physiological status of its associated bacterial communities. Unlike terrestrial material, sympagic algae that had escaped zooplanktonic grazing appeared relatively preserved from biotic degradation in Arctic sediments. The expected reduction in sea ice cover resulting from global warming should cause a shift in the relative contributions of ice-associated vs. pelagic algae to the seafloor, and thus to a strong modification of the carbon cycle.

Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration, and the source of Cr, Pb, and As might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao.

Total Petroleum Hydrocarbons Contamination of the Surface Water and Sediments of Orashi River, Engenni, Ahoada West, Rivers State, Nigeria

The level of contamination of Orashi River by total petroleum hydrocarbons were investigated through the collection of surface water samples and sediment samples from four locations along the river. Determination of the level of contamination was done with the use of gas chromatography-flame ionization detector after following laid down clean-up procedures. The results obtained showed that total petroleum hydrocarbons in the surface water were 10.913±2.2022mg/L, 7.645±2.683mg/L, 9.074±2.1654mg/L and 12.212±3.3034mg/L for stations 1, 2, 3 and 4 respectively with a mean value of 9.961±2.5885mg/L, while in the sediment samples concentration values recorded were 22.3925±5.2104mg/Kg, 35.1071±9.9652mg/Kg, 50.4431±15.9916mg/Kg and 29.3869±8.0410mg/Kg for stations 1, 2 3 and 4 respectively with a mean value of 34.3324±9.8021mg/Kg. The partition coefficient calculations revealed that the sediment phase is more stable for total petroleum hydrocarbons as compared to the water phase. The analysis of the randomly collected samples revealed that total petroleum hydrocarbons have contaminated the river and therefore adequate steps should be taken to remedy the present condition of the Orashi River in order to mitigate any probable rise in the quantity of total petroleum hydrocarbons in the river above allowable limit.

Development of an improved ramped pyrolysis method for radiocarbon dating and application to Antarctic sediments

<p>Archives of the retreat history of the Antarctic Ice Sheet since the Last Glacial Maximum (~20,000 years ago) are preserved in marine sediment cores from around the margins of Antarctica, but accurate dating methods remain elusive in many areas. Radiocarbon dating of key lithofacies transitions indicative of grounding-line retreat is problematic due to pervasive reworking issues in glacimarine sediments. Bulk sediment material can be radiocarbon dated but yields ages which are not indicative of the time of sedimentation due to the presence of reworked carbon material from pre-Last Glacial Maximum times. Consequently, development of methods to date only the autochthonous carbon component of these sediments are required to date the retreat of the Last Glacial Maximum ice sheet in Antarctica. A new radiocarbon dating capability has been developed at Rafter Radiocarbon Laboratory (RRL), National Isotope Centre, GNS Science, Lower Hutt, in the course of this study. This has entailed designing, building and testing a ramped pyrolysis (RP) system, in which sedimentary material is heated from ambient to ~1000oC in the absence of oxygen (pyrolysed), with the carbon liberated during pyrolysis being combined with oxygen at a temperature of ~800oC to produce CO2. The amount of CO2 produced is measured by a gas analyser and the CO2 is captured in a vacuum line. The method exploits the thermochemical behaviour of degraded organic carbon. Organic carbon which has been least degraded with time breaks down earliest under pyrolysis, so CO2 captured from this fraction most closely approximates the time of deposition of the sediment. CO2 captured at higher temperatures represents more degraded carbon-containing fractions and yields older ages. The RP system includes a gas delivery system to deliver ultra-high purity He (carrier gas) and O2, a furnace system in which to pyrolyse sample material and oxidise the liberated carbon, a CO2 detection system to measure the CO2 produced and a vacuum line system to enable simultaneous collection and processing of CO2. The RRL system was based on the design developed by Dr Brad Rosenheim (University of South Florida (USF)), the originator of the first RP system at the National Ocean Sciences AMS Facility (Woods Hole Oceanographic Institution, Massachusetts, USA), who also provided guidance in this thesis. As part of the study, a visit to USF was undertaken, with sediment samples from Crystal Sound, Antarctic Peninsula being processed in the USF RP system. CO2 collected from RP processing was radiocarbon dated at RRL. The scope of this thesis was to develop and build the RRL RP system, and numerous tests were conducted during this process and are presented in this thesis. As part of this, sediment samples from Crystal Sound were also processed on the RRL RP system, and an interlaboratory comparison was conducted on the same materials processed independently through both the USF and RRL RP systems. In the development and testing of the RRL system, numerous issues were identified and a set of operating protocols developed. Due to time constraints and the scope of this thesis, interlaboratory comparisons were limited in number, but initial results show good reproducibility, and that ramped pyrolysis captured significantly younger carbon populations in both the USF and RRL RP systems than methods using bulk sediment dating alone. Within uncertainties, the ages of the youngest and oldest splits from RP processing of the same material on both systems were indistinguishable.</p>