Fetal methylmercury exposure as measured by cord blood mercury concentrations in a mother-infant cohort in Hong Kong

This study was designed to examine newborn infants in Hong Kong prenatally exposed to levels of methylmercury considered to increase risk of neurotoxic effects and to examine subject characteristics that modify the degree of prenatal mercury exposure. Mercury concentrations in 1057 sets of maternal and cord blood samples and 96 randomly selected maternal hair samples were measured. Subject characteristics were measured or collected by questionnaire. Of the 1057 cord blood samples collected only 21.6% had mercury concentrations less than 29 nmol/L (5.8 micro g/L). Median maternal hair mercury concentration was 1.7 ppm. The geometric mean cord to maternal blood mercury ratio was 1.79 to 1. Increasing maternal fish consumption and maternal age were found to be associated with increased cord blood mercury concentrations. Marine fish consumption increased cord blood mercury concentrations more than freshwater fish (5.09%/kg vs 2.86%/kg). Female babies, maternal alcohol consumption and increasing maternal height were associated with decreased cord blood mercury concentrations. Pregnant women in Hong Kong consume large amounts of fish and as a result, most of their offspring have been prenatally exposed to moderately high levels of mercury. In this population, pregnant women should choose freshwater over marine fish and limit fish consumption.     

Prolonged exposure to low dissolved oxygen affects early development and swimming behaviour in the gastropod Nassarius festivus (Nassariidae)

Effects of low dissolved oxygen on early development and swimming behaviour of veliger larvae of the scavenging gastropod Nassarius festivus were studied. Embryonic development was significantly delayed when dissolved oxygen level was reduced to 3.0 mg O₂ l⁻¹ and no embryo hatched successfully at 0.5 mg O₂ l⁻¹. Veliger larvae hatched at 4.5 mg O₂ l⁻¹ had significantly smaller velar lobe, shell length and shell width. Median 48-h LC₅₀ value of the veliger larvae was estimated at 1.25 mg O₂ l⁻¹ with lower swimming speed (swimming velocity and dispersal velocity) being recorded for the survivors exposed to reduced oxygen levels. The percentage of veliger larvae that developed into crawling juveniles was significantly reduced and metamorphosis was delayed at 4.5 mg O₂ l⁻¹ whereas all larvae at 3.5 mg O₂ l⁻¹ died before they underwent metamorphosis. Juveniles developed at 4.5 mg O₂ l⁻¹ were also smaller than those at 6.0 mg O₂ l⁻¹. Results indicated that dissolved oxygen levels well above hypoxia levels (2.8 mg O₂ l⁻¹) have already had significant impact on the hatching success and larval development in gastropods, which may lead to long-term decreases in population growth.     

Experimental investigation of regulated and unregulated emissions from a diesel engine fueled with Euro V diesel fuel and fumigation methanol

Experiments were conducted on a four-cylinder direct-injection diesel engine with part of the engine load taken up by fumigation methanol injected into the air intake of each cylinder to investigate the regulated and unregulated gaseous emissions and particulate emission of the engine under five engine loads at an engine speed of 1920 rev min^?1. The fumigation methanol was injected to top up 10%, 20% and 30% of the engine load under different engine operating conditions.The experimental results show that at low engine loads, the brake thermal efficiency (BTE) decreases with increase in fumigation methanol; but at high engine loads, the BTE is not significantly affected by fumigation methanol. The fumigation methanol results in significant increase in hydrocarbon (HC), carbon monoxide (CO) and nitrogen dioxide (NO₂) emissions, but decrease in nitrogen oxides (NO_x). For the unregulated gaseous emissions, unburned methanol, formaldehyde and BTX (benzene, toluene and xylene) emissions increase but ethyne, ethene and 1,3-butadiene emissions decrease. Particulate mass and number concentrations also decrease with increase in fumigation methanol. A diesel oxidation catalyst (DOC) is found to reduce significantly most of the pollutants, including the air toxics, when the exhaust gas temperature is sufficiently high.     

Perceptions of implied hazard for visual and auditory alerting signals

Visual and auditory alerts are increasingly important and have many applications, particularly in the presentation of hazard information in transportation and many industrial systems. This paper is concerned with the factors that govern the relative effectiveness of alerting signals involving various combinations of visual and auditory signals. The visual variables were colour, flash rate, and flash mode, combined with or without an auditory alarm. It was found that the subjects associated different levels of hazard with different alerting light colours, flash rates, flashing modes, and with combinations of auditory and visual alerts. A red flashing light was perceived as the most effective hazard warning colour, with yellow and blue warning lights indicative of less hazardous situations. The faster the flash rate, the greater is the hazard perceived. A flash rate of 60 fpm (flashes per minute) was not as effective as the rates of 180 and 240 fpm, and 240 fpm was the most effective. This implies that hazard warning signal should flash at well above 60 fpm. Having a breakup in the flashing pattern so as to provide a double or triple flash mode also increases the effectiveness of the signal. There were significant interactions between the alert variables used. The difference in perceived hazard levels for the colours blue and yellow were statistically non significant, but blue was more effective in conveying hazard message than yellow at the high flash rates. When accompanied with auditory alarms, blue and yellow were perceived to convey the same perception level of hazard as red without auditory alarms. The effect of colour on perceived hazard was also found to vary with flash mode. As compared to either visual signal alone or a visual signal with other types of acoustic alarms, a siren type of auditory alarm was found more effective for eliciting perception of hazards. There was evidence that presenting alerting signal in triple-flash mode and at high flash rate could be annoying and might not help improving hazard awareness.     

Use of ammoniacal nitrogen tolerant microalgae in landfill leachate treatment

Two microalgae, Chlorella pyrenoidosa and Chlamydomonas snowiae, were isolated from a high ammonia leachate pond in Li Keng Landfill, Guangzhou, China. Their growth and nutrient removal rates were determined in a serial dilution of landfill leachate under laboratory conditions, and their growth rates were compared with that of a C. pyrenoidosa strain isolated from a clean river. The results indicated the growth of all three algae was inhibited by high leachate concentrations, and the inhibition appears linked to high ammonia (ammoniacal-N670mgL(-1)). Significant amounts of ammoniacal-N, ortho-P and COD in the leachate were removed by the algae, with a positive correlation between algal growth and nutrient consumption. Not enough data are available to conclude that one strain was less inhibited by ammoniacal nitrogen or more effective at treating it. Phytotoxicity of leachate was reduced after algal growth, as demonstrated by a seed germination experiment with Brassica chinensis. The germination rates in 10%, 30% and 50% concentrations of algal-treated leachate were significantly higher than those in the same concentration but algal-free leachate.     

Solubilization of blood meal to be used as a liquid fertilizer

The solubilization of blood meal by means of the microwave-hydrogen peroxide enhanced advanced-oxidation process (MW/H(2)O(2)-AOP) was studied. It was found that over the treatment temperature range of 60 to 120 degrees C, solids particle reduction, ammonia and orthophosphate production could be achieved by this process. Large protein molecules were broken down into intermediate compounds with low molecule weights, ammonia and nitrate. Intermediate compounds, such as peptides and amino acids, can also be easily converted to nitrogenous nutrients for plant growth by bacteria. Soluble nitrogen content increased with an increase in microwave heating temperature when acid was added; significant amounts of ammonia were obtained at higher temperatures. Nitrate decreased in concentration with an increase of treatment temperature. Orthophosphate concentrations increased after the advanced-oxidation process (AOP) treatments, with and without acid addition; but were more pronounced with acid addition. Maximum solubility of chemical oxygen demand (COD) occurred at 80 degrees C. Without the addition of acid, soluble COD decreased due to protein denaturation and coagulation out of the solution.     

Elimination of 10 polybrominated diphenyl ether (PBDE) congeners and selected polychlorinated biphenyls (PCBs) from the freshwater mussel, Elliptio complanata

Mussel biomonitors are widely used as screening tools for polybrominated diphenyl ethers (PBDEs) in marine and aquatic environments. This study determined elimination rate coefficients (k(tot)) for eight PBDE and five PCB congeners in the freshwater mussel, Elliptio complanata, over a 120d depuration period. Elimination of BDE 15, 28, 47, 75 and 100 was similar to PCBs of equivalent hydrophobicity and negatively related to chemical K(OW). Rapid elimination of BDE 190 and an inferred rapid elimination of BDE 183 indicate mussels are capable of biotransformation of certain highly brominated PBDEs. Time to 90% steady state ranged from 48 to 66d for di- and tribromoDE congeners and from 91 to >250d for tetra- to hexabromoDE congeners. Given the long time periods required for steady state, mussel accumulated PBDE residues should be interpreted in the context of calibrated bioaccumulation models.     

Recovery of benthic invertebrate communities from acidification in Killarney Park lakes

Using a reference-condition comparison, recovery of benthic invertebrate communities from acidification was assessed in three lakes in Killarney Wilderness Park approximately 40–60 km from the massive metal smelters in Sudbury, Canada. Test site analyses (TSAs) were used to compare the park lakes to 20 reference lakes near Dorset Ontario, 200 km to the east. An extension of a previous survey (1997–2001) of two sensitive mayfly species (Stenonema femoratum and Stenacron interpunctatum) was conducted in one of the lakes. TSA results indicate that the three Killarney lakes remain significantly different from reference condition due primarily to higher abundances of a few acid-tolerant families and the presence of some less abundant sensitive families. Colonization rates differ greatly between the two mayfly species presumably because of competition for available habitat. Overall, this study suggests that early colonizers will gain an advantage to out-compete subsequent arrivals, and these competitive interactions will delay the return of communities to reference condition.     

Characteristics and sources of non-methane hydrocarbons and halocarbons in wintertime urban atmosphere of Shanghai, China

The characteristics and sources of major hydrocarbons and halocarbons in the wintertime ambient air of urban center of Shanghai, a mega city of China, were investigated. Propane, toluene, ethyl acetate, and benzene were the most abundant hydrocarbons. The majority of species showed significant variability in mixing ratios with occasional episodic increases. The more common use of liquefied petroleum gas fuel for taxis and light motorcycles was believed to lead to high levels of ambient propane over the urban center of Shanghai. Correlating with toluene, dichloromethane, and 1,2-dichloroethane (1,2-DCE), abundant chloromethane (up to a daily mean of 1.61?±?0.99 ppbv and a maximum of 5.34 ppbv) was mainly associated with industrial emissions, although biomass burnings exist widely in east China. The Chinese New Year (CNY) holiday period with no industrial activity over China provides a platform for the study of industrial emissions over the urban atmosphere of Shanghai. The normal weekly cycles were characterized by higher and more variable mixing ratios during weekdays which dropped during weekends. Enhanced mixing ratios were observed in the fortnight before the CNY holidays due to increased industrial emissions as a result of overtime production to make up for the holiday losses. During the CNY holidays, lower level and less variable mixing ratios were observed. A benzene/toluene (B/T) ratio of 0.6?±?0.4 (mean?±?std.) for the morning rush hour samples was identified to be the characteristic ratio of vehicular emissions. However, a B/T ratio of 0.4?±?0.2 from vehicles and other sources was derived for the ambient air.     

Dynamic regression modeling of daily nitrate-nitrogen concentrations in a large agricultural watershed

Nitrate-nitrogen concentrations in rivers represent challenges for water supplies that use surface water sources. Nitrate concentrations are often modeled using time-series approaches, but previous efforts have typically relied on monthly time steps. In this study, we developed a dynamic regression model of daily nitrate concentrations in the Raccoon River, Iowa, that incorporated contemporaneous and lags of precipitation and discharge occurring at several locations around the basin. Results suggested that 95 % of the variation in daily nitrate concentrations measured at the outlet of a large agricultural watershed can be explained by time-series patterns of precipitation and discharge occurring in the basin. Discharge was found to be a more important regression variable than precipitation in our model but both regression parameters were strongly correlated with nitrate concentrations. The time-series model was consistent with known patterns of nitrate behavior in the watershed, successfully identifying contemporaneous dilution mechanisms from higher relief and urban areas of the basin while incorporating the delayed contribution of nitrate from tile-drained regions in a lagged response. The first difference of the model errors were modeled as an AR(16) process and suggest that daily nitrate concentration changes remain temporally correlated for more than 2 weeks although temporal correlation was stronger in the first few days before tapering off. Consequently, daily nitrate concentrations are non-stationary, i.e. of strong memory. Using time-series models to reliably forecast daily nitrate concentrations in a river based on patterns of precipitation and discharge occurring in its basin may be of great interest to water suppliers.