Baseline concentrations and distributions of Polycyclic Aromatic Hydrocarbons in surface sediments from the Qatar marine environment.

Coastal sediments in marine waters of Qatar have the potential of being contaminated by Polycyclic Aromatic Hydrocarbons (PAHs) due to extensive petroleum exploration and transportation activities within Qatar's Marine Exclusive Economic Zone. In this study, the concentration and distribution of sixteen PAHs classed as USEPA priority pollutants were measured in sediments from the eastern Qatari coast. PAHs were recovered from sediments via accelerated solvent extraction and then analyzed using Gas Chromatography-Mass Spectrometry. Total concentrations of the PAHs were in the range of 3.15-14.35µg/kg, and the spatial distribution of PAHs is evaluated in the context of sediment total organic content, depth and the grain size together with and the proximity of petroleum exploration and transportation activities. The data show that the concentrations of PAHs within the study area were in the low-range, suggesting a low risk to marine organisms and limited transfer of PAHs into the food web.

Microplastics in coastal environments of the Arabian Gulf.

Eight sandy beaches along the coastline of Qatar and four sea surface stations on the eastern coast, adjacent to Doha Bay, were surveyed between December 2014 and March 2015. Microplastics, mainly low density polyethylene and polypropylene, were found in all samples of sediments and seawater. Blue fibers, ranging between 1 and 5mm, were the dominant type of particle present. Abundances on the sea surface varied between 4.38×104 and 1.46×106particles·km-2, with the highest values being consistently found 10km offshore, suggesting the presence of a convergence zone. No significant temporal variability was detected for sea surface samples. The concentration of microplastics in intertidal sediments varied between 36 and 228particlesm-2, with no significant differences among the 8 beaches examined. These results show the pervasiveness of microplastic pollution in coastal environments of the Arabian Gulf. Potential local sources and sinks for microplastics are discussed.

Prevalence of microplastics in the marine waters of Qatar.

Microplastics are firmly recognized as a ubiquitous and growing threat to marine biota and their associated marine habitats worldwide. The evidence of the prevalence of microplastics was documented for the first time in the marine waters of Qatar's Exclusive Economic Zone (EEZ). An optimized and validated protocol was developed for the extraction of microplastics from plankton-rich seawater samples without loss of microplastic debris present and characterized using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy. In total 30 microplastic polymers have been identified with an average concentration of 0.71particlesm(-3) (range 0-3particlesm(-3)). Polypropylene, low density polyethylene, polyethylene, polystyrene, polyamide, polymethyl methacrylate, cellophane, and acrylonitrile butadiene styrene polymers were characterized with majority of the microplastics either granular shape, sizes ranging from 125µm to 1.82mm or fibrous with sizes from 150µm to 15.98mm. The microplastics are evident in areas where nearby anthropogenic activities, including oil-rig installations and shipping operations are present.

Microplastics in Singapore's coastal mangrove ecosystems.

The prevalence of microplastics was studied in seven intertidal mangroves habitats of Singapore. Microplastics were extracted from mangrove sediments via a floatation method, and then counted and categorized according to particle shape and size. Representative microplastics from Berlayar Creek, Sungei Buloh, Pasir Ris and Lim Chu Kang were isolated for polymer identification using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. Microplastics were identified in all seven habitats, with the highest concentration found in sediments at Lim Chu Kang in the northwest of Singapore. The majority of microplastics were fibrous and smaller than 20 µm. A total of four polymer types were identified, including polyethylene, polypropylene, nylon and polyvinyl chloride. The relationship between abundance of microplastics and sediment grain size was also investigated, but no relationship was apparent. The presence of microplastics is likely due to the degradation of marine plastic debris accumulating in the mangroves.

Application of mid-infrared chemical imaging and multivariate chemometrics analyses to characterise a population of microalgae cells.

A suite of multivariate chemometrics methods was applied to a mid-infrared imaging dataset of a eustigmatophyte, marine Nannochloropsis sp. microalgae strain. This includes the improved leader-follower cluster analysis (iLFCA) to interrogate spectra in an unsupervised fashion, a resonant Mie optical scatter correction algorithm (RMieS-EMSC) that improves data linearity, the band-target entropy minimization (BTEM) self-modeling curve resolution for recovering component spectra, and a multi-linear regression (MLR) for estimating relative concentrations and plotting chemical maps of component spectra. A novel Alpha-Stable probability calculation for microalgae cellular lipid-to-protein ratio Λi is introduced for estimating population characteristics.

Incremental energy supply for microalgae culture in a photobioreactor.

A model was developed for any PBR, based on mixing requirement per unit of biomass production rather than constant amount of mixing energy. The model assumes constant biomass concentration throughout the culture time which means the volume of the culture would increase over time; the mixing energy will also increase over time according to the volume of the culture. Such incremental energy supply (IES) consumes much less energy compared to constant energy supply (CES); higher the culture time in the PBR, more is the savings in the IES compared to CES. In addition to mixing energy, light energy can also be applied using IES scheme. The model was validated with the algae Nannochloropsis sp.; 44% of the energy input of CES was saved by adopting IES with equal biomass productivities for a culture period of 60 h.

Heterogeneous catalytic transesterification of phosphatidylcholine.

The transesterification of phosphatidylcholine (PC) via homogeneous and heterogeneous catalysis was investigated for the production of fatty acid methyl esters (FAME) i.e. biodiesel. Calcium methoxide and calcium oxide were used as heterogeneous catalysts, and KOH as a homogeneous catalyst for the transesterification of phosphatidylcholine (PC)--a polar phospholipid prevalent in eukaryotic organisms. The initial reaction rate was higher for KOH (24.23 g of FAME/g of catalyst.min) than for calcium methoxide (17.06 g of FAME/g of catalyst.min) and calcium oxide (1.06 g of FAME/g of catalyst.min). PC was then mixed with soybean oil at different proportions (i.e. 10%, 30% and 50%, PC10, PC30 and PC50, respectively) which was then used as the feedstock for transesterification using calcium methoxide. When the mass fraction of PC was increased in the feedstock reaction rate also increased. Phosphorus content of the FAME layer of PC100, PC50, PC30 and PC10 was 0.081, 0.041, 0.035 and 0.028% (w/w), respectively.

Enhanced algae growth in both phototrophic and mixotrophic culture under blue light.

Biomass productivity and fatty acid methyl esters (FAME) derived from intracellular lipid of a Nannochloropsis sp. isolated from Singapore's coastal waters were studied under different light wavelengths and intensities. Nannochloropsis sp., was grown in both phototrophic and mixotrophic (glycerol as the carbon source) culture conditions in three primary monochromatic light wavelengths, i.e., red, green and blue LEDs, and also in white LED. The maximum specific growth rate (µ) for LEDs was blue>white>green>red. Nannochloropsis sp. achieved a µ of 0.64 and 0.66 d(-1) in phototrophic and mixotrophic cultures under blue lighting, respectively. The intracellular fatty acid composition of Nannochloropsis sp. varied between cultures exposed to different wavelengths, although the absolute fatty acid content did differ significantly. Maximum FAME yield from Nannochloropsis sp. was 20.45% and 15.11% of dry biomass weight equivalent under photo- and mixotrophic culture conditions respectively for cultures exposed to green LED (550 nm). However, maximum volumetric FAME yield was achieved for phototrophic and mixotrophic cultures (i.e., 55.13 and 111.96 mg/l, respectively) upon cell exposure to blue LED (470 nm) due to highest biomass productivity. It was calculated that incremental exposure of light intensity over the cell growth cycle saves almost 20% of the energy input relative to continuous illumination for a given light intensity.

Exposure to persistent organic pollutants in utero and related maternal characteristics on birth outcomes: a multivariate data analysis approach.

Persistent organic pollutants (POPs) have the capacity to pass through the placental barrier and into the fetal blood stream, and pose health risks to fetuses and neonates who are believed to be more vulnerable to the effects of environmental pollutants. In this study, the prevalence of POPs, including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated biphenyl ethers (PBDEs), were determined in 41 cord blood samples collected during the year 2006 in Singapore. The effects of these xenobiotics and the maternal characteristics on fetal growth and development were explored using multivariate data analysis (MVA) techniques, including partial least-squares regression (PLSR) and discriminant analysis (PLS-DA). POPs were found in all cord blood samples, corroborating the transplacental transfer (TPT) of these xenobiotics. Chlordanes and PCBs were observed to have adverse effects on fetal growth (i.e. birth weight, length, head circumference) and health (as indicated by Apgar scores), indicating the chemical exposure in utero could also be deemed as an influential factor on fetal growth, even at the normal doses in general population. Maternal height, weight, ethnicity, dietary habits and lifestyle were also the determinants for the neonatal variables. Exposure to POPs may alter maternal hormone levels, which could regulate the offspring sex. Trans-chlordane, p,p'-DDE, p,p'-DDT and PCB 138 and 158 were speculated as testosterone triggers which lead to more baby boys, while the effects of beta-HCH and PCB 180 were opposite.

Multivariate data analyses of persistent organic pollutants in maternal adipose tissue in Singapore.

Persistent organic pollutants (POPs) were detected in 88 maternal adipose tissue samples collected during year 2004 to 2006, in Singapore. Organochlorine pesticides (OCPs) were the most dominant followed by polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). Multivariate data analyses (MVA) including principal component analysis (PCA), partial least-squares regression (PLSR), and partial least-squares discriminant analysis (PLS-DA) were applied to elucidate the relationship between concentrations of POPs in adipose tissues and donors' characteristics. Food consumption played the most significant role in accounting for levels of POPs in adipose tissue. Fish and poultry consumption was the route of PCBs and PBDEs in mothers in Singapore, while beta-HCH came mainly from vegetables. An age-dependent accumulation of POPs was found for beta-HCH and PCB congeners, and lactation and gestation functioned as a decontamination processes for PCBs in adipose tissue. Gestational diabetes mellitus (GDM) may change the profile of POPs in adipose tissue, probably due to an alteration in lipid metabolism. POPs investigated here may not be the cause of antenatal complication in pregnant women, and baby gender was not related to the pattern of contaminants in maternal adipose tissue.

Distribution of heavy metals in the dissolved and suspended phase of the sea-surface microlayer, seawater column and in sediments of Singapore's coastal environment.

Concentrations of heavy metals were determined in the water column (including the sea-surface microlayer, subsurface, mid-depth and bottom water) and sediments from Singapore's coastal environment. The concentration ranges for As, Cd, Cr, Cu, Ni, Pb and Zn in the seawater dissolved phase (DP) were 0.34-2.04, 0.013-0.109, 0.07-0.35, 0.23-1.16, 0.28-0.78, 0.009-0.062 and 0.97-3.66 microg L(-1) respectively. The ranges for Cd, Cr, Cu, Ni, Pb and Zn in the suspended particulate matter (SPM) were 0.16-0.73, 6.72-53.93, 12.87-118.29, 4.34-60.71, 1.10-6.08 and 43.09-370.49 microg g(-1), respectively. Heavy metal concentrations in sediments ranged between 0.054-0.217, 37.48-50.52, 6.30-21.01, 13.27-26.59, 24.14-37.28 and 48.20-62.36 microg g(-1) for Cd, Cr, Cu, Ni, Pb and Zn, respectively. The lowest concentrations of metals in the DP and SPM were most frequently found in the subsurface water while the highest concentrations were mostly observed in the SML and bottom water. Overall, heavy metals in both the dissolved and particulate fractions have depth profiles that show a decreasing trend of concentrations from the subsurface to the bottom water, indicating that the prevalence of metals is linked to the marine biological cycle. In comparison to data from Greece, Malaysia and USA, the levels of metals in the DP are considered to be low in Singapore. Higher concentrations of particulate metals were reported for the Northern Adriatic Sea and the Rhine/Meuse estuary in the Netherlands compared to values reported in this study. The marine sediments in Singapore are not heavily contaminated when compared to metal levels in marine sediments from other countries such as Thailand, Japan, Korea, Spain and China.

A modified technique for field measurements of dry deposition fluxes of polychlorinated biphenyls in tropical regions.

This report focused on the development of a technique to measure dry deposition fluxes of PCBs in tropical environments. Temperature resistant double-adhesive tape has been used as a new surrogate surface for collection of deposited PCBs. The new technique includes the measurement of field blanks for the entire sampling period. A sonication-assisted extraction procedure has been validated for the extraction of PCBs from the tape. The new technique has been used in the field for a period of 4 months in the tropical region of Singapore. The average dry deposition flux measured for total PCBs was 15.3 ng m(-2) day(-1) and, on a global scale, this can be considered to be low.

Atmospheric wet deposition of PAHs to the sea-surface microlayer.

Sea-surface microlayer (SML) and subsurface seawater samples (SSW) collected from Singapore's coastal environment were analyzed for 14 polycyclic aromatic hydrocarbons (PAHs) in the dissolved (DP) and suspended particulate phase (SPM). Samples were collected prior to and after rainfall events to ascertain the contribution of wet atmospheric deposition of PAH enrichment to the SML. The concentration ranges of summation operatorPAHs in the SML before rain and after wet deposition were 2.6-46.2 ngL(-1) and 4.3-278.0 ngL(-1), respectively, for the DP and 3.8-31.4 ngL(-1) and 12.8-1280 ngL(-1), respectively, for the SPM. Load factors (i.e. concentration after wet deposition relative to before wet deposition) of the atmospheric wet deposition for DP and SPM ranged from 1.4 to 42.9 and 1.2 to 337, respectively. This study provides the first data on PAH concentration, enrichment (i.e. concentration of PAHs in SML relative to subsurface water) and load factors in the SML before and after wet deposition to the ocean surface.

Selected organochlorine pesticide and polychlorinated biphenyl residues in house dust in Singapore.

Although the use of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) has been prohibited in Singapore since 1980, OCPs and PCBs still can be detected in the environment and represent a potential threat to public health. In this study, OCPs and PCBs were measured in house dust samples collected from 31 homes across the island-state of Singapore. Organochlorine pesticides, such as hexachlorocyclohexanes (HCHs), chlordanes and dichlorodiphenyltrichloroethanes (DDTs) were tested, with a range of

Polybrominated diphenyl ethers in house dust in Singapore.

The use of polybrominated diphenyl ethers (PBDEs) as flame retardants in Singapore is not strictly regulated; therefore these compounds can be readily found in furniture, electronic devices, and building materials. This study was the first of its kind to be conducted in Singapore to measure concentrations of PBDEs in house dust. Samples were collected from 31 homes in various locations across the island-state of Singapore, and a total eight PBDEs congeners were measured. PBDEs were detected in all 31 dust samples and the number of BDE congener detected per home ranged between 3 and 8. The most abundant BDE congeners found were BDE 47, 99 and 209, with a median value of 20 ng g(-1) dust, 24 ng g(-1) dust and 1000 ng g(-1) dust, respectively. BDE 209 contributed 88% to the median of all the congeners, and BDE 47 and 99 contributed 1.8% and 3.5%, respectively. Different congener profiles were observed between this and studies conducted elsewhere, which is consistent with the use of different commercial PBDE around the world. No significant correlations between PBDE dust levels and residential characteristics (number of TVs and computers, floor area or flooring material) were observed. The daily intake of PBDEs via the inhalation pathway was estimated. House dust may be regarded as the most important exposure route of PBDEs for children.

Levels of persistent organic pollutant residues in human adipose and muscle tissues in Singapore.

Persistent organic pollutants (POPs), due to their persistence and bioconcentration in lipid-rich tissue, bioaccumulate in food chains, resulting in elevated concentrations in humans. This study was performed to determine and compare levels of POPs in human adipose and muscle tissues in the female population of Singapore. In total, 36 human adipose tissues and 8 human muscle tissues were collected from volunteer expectant mothers admitted to the National University Hospital Singapore for cesarean section delivery between August 2003 and January 2005. Samples were analyzed using a validated and quality-assured gas chromatography-mass spectroscopy (GC-MS) method in conjunction with microwave-assisted extraction (MAE). Analytes recoveries from certified reference materials, that is, IRMM-446 (polychlorinated biphenyls [PCBs] in pork fat) and BCR-430 (organochlorine pesticides in pork fat), were between 70 and 130%, indicating reliable analytical precision for this methodology. MAE efficiency for polybrominated diphenyl ethers (PBDEs) was compared to Soxhlet extraction (SE) efficiency and yielded comparable results (variation < 13%). Analytical results indicate that p,p'-DDE of the dichlorodiphenyltrichloroethane (DDT) residues group is the predominant compound in adipose tissue, followed by beta-hexachlorocyclohexane (beta-HCH) among HCH isomers, then hexachlorobenzene (HCB) compound and specific PCB and PBDE congeners. Among the 36 adipose tissues, the lipid contents in adipose tissue were in the range of 60% to 95%, while in the 8 muscle tissues, lipids were undetectable. However, the profile of PCBs and pesticide residues present in muscle tissues were similar to those in adipose tissues.

Persistent organic pollutants and adverse health effects in humans.

Persistent organic pollutants (POPs) are synthetic chemicals that have an intrinsic resistance to natural degradation processes, and are therefore environmentally persistent. The introduction of POPs into the environment from anthropogenic activities resulted in their widespread dispersal and accumulation in soils and water bodies, as well as in human and ecological food chains, where they are known to induce toxic effects. Due to their ubiquity in the environment and lipophilic properties, there is mounting concern over the potential risks of human exposure to POPs. This has led to the establishment of monitoring programs worldwide to determine prevailing levels of POPs in the population and to investigate the adverse health risks associated with background exposure. This article reviews the state of knowledge regarding residual levels of POPs in human adipose tissue worldwide, and highlights research data for POPs in the environment and human maternal adipose tissue in Singapore. Although concentrations are comparable to those observed elsewhere, longer term monitoring of a larger cross section of the population is warranted in order to establish temporal trends and potential risks to human health.

Chlorinated paraffins: a review of analysis and environmental occurrence.

Chlorinated paraffins (CPs), as technical mixtures of polychlorinated alkanes (PCAs), are ubiquitous in the environment. CPs tend to behave in a similar way to persistent organic pollutants (POPs), leading several countries to impose regulations on the use of CPs. In this article, we review the literature on the properties of CPs, the current analytical tools available to determine CPs in various types of environmental matrices, and concentrations found in the environment. In particular, concentrations of CPs in environmental compartments including air, water, sediments, biota, human food products and human tissues are summarized. Priorities for future research are: improvements in analytical methodologies (reducing the complexity of the analysis, producing reference materials and performing interlaboratory studies); determining background levels of chlorinated paraffins in the environment and human populations (this question should be answered using quality assured analytical tools allowing the intercomparison of data); and investigating the sources of CPs to the environment and to humans.

The role of the sea-surface microlayer in the air-sea gas exchange of organochlorine compounds.

Simultaneous measurements of organochlorine compounds (OCs) in seawater, the sea-surface microlayer and the atmosphere were conducted in June-July 2004 in the coastal marine environment of Singapore. Together, these measurements represent the first data on the flux of OCs between the ocean and atmosphere reported in the scientific literature that take into account the implication of the sea surface microlayer (SML) as a controlling boundary layer for the exchange of OCs. The average fluxes of SigmaPCBs and SigmaHCHs were 127.5 and -32.8 ng m(-2) day(-1) respectively using a modified two-layer model (negative flux indicates adsorption by the ocean). The average fluxes using a conventional approach, ignoring the SML as boundary layer (classical two-layer model), were 67.2 and -43.1 ng m(-2) day(-1) for SigmaPCBs and SigmaHCHs, respectively. However, the maximum difference in the flux calculation between the two approaches was up to 15-fold for individual compounds at high enrichment in the SML. It is shown that the SML plays an important role in the control of air-sea gas exchange of OCs, particular under a low prevailing wind regime and with an enrichment of OCs in the SML. The physical and chemical properties of OCs are critical factors in the control of the air-sea gas exchange process, and the effect of the SML on this process is more significant for more hydrophobic OCs.

Persistent organic pollutants in the equatorial atmosphere over the open Indian Ocean.

Twelve air samples collected over the Indian Ocean by a high volume air sampler between August 2004 and August 2005 were analyzed for selected polychlorinated biphenyl (PCB) congeners and organochlorine pesticides. The region of the Indian Ocean and adjacent countries is likely to be acting as a source of selected POPs to the global environment. Data were compared with those reported for the last 30 years to examine historical trends of selected persistent organic pollutants (POPs) over the Indian Ocean. Compound concentrations were influenced by the proximity to land and air mass origins. Higher concentrations of atmospheric sigmaPCBs (50-114 pg m(-3)) were found on the remote islands of Chagos Archipelago and Gan, Maldives, and in the proximity of Jakarta, Indonesia, and Singapore. Military activities and unregulated waste combustion were identified as possible sources for atmospheric PCB contaminations at the more remote areas. The highest concentrations of organochlorine pesticides were found adjacent to the coastline of Sumatra and Singapore, where sigmaDDTs (dichlorodiphenyltrichloroethane) and sigmaHCHs (hexacyclohexanes) were as high as 30 and 100 pg m(-3), respectively. A comparison study for the last 30 years over six regions of the Indian Ocean showed that the concentrations of organochlorine pesticides have declined significantly, by a magnitude of two, since the mid 1970s, but were highest at the beginning of the 1990s. The time trend of PCB contamination in the atmosphere over the Indian Ocean is less apparent. The decline of atmospheric POPs over the Indian Ocean may be due to international regulation of the use of these compounds.