Air–water exchange fluxes of polycyclic aromatic hydrocarbons in the tropical coast,Taiwan

Air–water exchange fluxes of polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured in air and water samples from two sites on the Kenting coast, located at the southern tip of Taiwan, from January to December 2010. There was no significant difference in the total PAH (t-PAH) concentrations in both gas and dissolved phases between these two sites due to the less local input which also coincided to the low levels of t-PAH concentration; the gas and dissolved phases averaged 1.29 ± 0.59 ng m^?3 and 2.17 ± 1.19 ng L^?1 respectively. The direction and magnitude of the daily flux of PAHs were significantly influenced by wind speed and dissolved PAH concentrations. Individual PAH flux ranged from 627 ng m^?2 d^?1 volatilization of phenanthrene during the rainy season with storm–water discharges raising dissolved phase concentration, to 67 ng m^?2 d^?1 absorption of fluoranthene during high wind speed periods. Due to PAH annual fluxes through air–water exchange, Kenting seawater is a source of low molecular weight PAHs and a reservoir of high molecular weight PAHs. Estimated annual volatilization fluxes ranged from 7.3 μg m^?2 yr^?1 for pyrene to 50 μg m^?2 yr^?1 for phenanthrene and the absorption fluxes ranged from ?2.6 μg m^?2 yr^?1 for chrysene to ?3.5 μg m^?2 yr^?1 for fluoranthene.     

Microwave-induced nanoscale zero-valent iron degradation of perchloroethylene and pentachlorophenol

Microwave (MW) is applied to enhance perchloroethylene (PCE) or pentachlorophenol (PCP) removal using zero-valent iron (ZVI; Fe⁰) as the dielectric medium. ZVI has a much higher dielectric loss factor (39.5) than other media; it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rises of the ZVI particle surface temperature. If the MW power is continued, excessive electricity will accumulated inside ZVI particles, resulting in sparks. The results show that during the initial 5 sec (700 W), the linear aliphatic PCE has a faster decomposing rate than the ringed PCP (82.0% vs. 4.8%) because less energy is required for decomposing the linear-chlorine bond (90 kcal mol^?1) than ring-chlorine bonds (95 kcal mol^?1). Later, the removal rate for either PCE or PCP remains the same when the exposure time is between 5 and 60 sec. Without MW irradiation, linear PCE molecules have larger surface area to contact ZVI, and hence they have better removal efficiencies than PCP molecules. Using Fe⁰ as a microwave dielectric medium to treat PCE or PCP is a new and worthwhile treatment technology; it is environmentally friendly, and its use will eliminate the secondary pollution.

Implications Nanoscale iron particles are characterized by high surface-area-to-volume ratios, high specific surface area, and high surface reactivity. With a much higher dielectric loss factor, it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rise in temperature. The time needed to achieve a satisfactory treatment is also reduced, leading to significant saving of energy consumption to make this method cost-effective and also environmentally friendly for the industry to pursuit sustainable development.     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.     

Non-renewable resource prices: Deterministic or stochastic trends?

In this paper, we examine temporal properties of 11 natural resource real price series from 1870 to 1990. Recent studies by Ahrens and Sharma [Trends in natural resource commodity prices: deterministic or stochastic? J. Environ. Econom. Manage. 33(1997)59–74], Berck and Roberts [Natural resource prices: will they ever turn up? J. Environ. Econom. Manage. 31(1996)65–78], and Slade [Grade selection under uncertainty: least cost last and other anomalies, J. Environ. Econom. Manage. 15(1988)189–205], among others, find that many non-renewable resource prices have a stochastic trend. We revisit this issue by employing a Lagrangian multiplier unit root test that allows for two endogenously determined structural breaks with and without a quadratic trend. Contrary to previous research, we find evidence against the unit root hypothesis for all price series. Our findings support characterizing natural resource prices as stationary around deterministic trends with structural breaks. We additionally show that both pre-testing for unit roots with breaks and allowing for breaks in the forecast model can improve forecast accuracy. Overall, the results in this paper are important in both a positive and normative sense; without an appropriate understanding of the dynamics of a time series, empirical verification of theories, forecasting, and proper inference are potentially fruitless.     

Metabolic response under different salinity and temperature conditions for glass eel Anguilla japonica

Diadromous fish often enter freshwater directly from seawater via fish ladders or channels built in estuarine dams. The oxygen consumption rates (OCR) of glass eel, Anguilla japonica, were determined using an automatic intermittent flow respirometer under various salinity and temperature regimes to physiologically explain this direct movement. The endogenous rhythm of the OCR in wild glass eels, freshly collected from estuaries, was nearly synchronous with the tidal pattern at the estuarine collection site. When the salinity was changed from 20 psu (12°C) at a constant temperature to that of freshwater, the OCR of the glass eels decreased by 21.6±7.0% (mean ± SD) (P<0.05), showing a dampened rhythm for about 48 h. After this period of impediment, the glass eels resumed normal metabolic activity. Direct migration from seawater to freshwater under constant temperature would result in a severe physiological stress for these glass eels for about two days. When the glass eels were exposed to a cyclic change in water temperature of 2°C 26 h⁻¹, as they encounter in estuaries, and then were introduced to freshwater abruptly, the OCR rhythm corresponded to the cyclic changes in water temperature after exposure to freshwater. Under these conditions, the mean OCR of the glass eels had a small difference before and after exposure to freshwater. These data explained how glass eels can directly move from sea water into the freshwater without any apparent metabolic stress in the estuaries showing cyclic change in water temperature (Δt=2°C).     

Mobilization of arsenic in groundwater of Bangladesh: evidence from an incubation study

The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(ΙΙ) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50–67 μg/l) and Fe(ΙΙ) (maximum: 182 μg/l), while the ORP value decreased immediately and drastically (as much as −468 mV to −560 mV) within 5–6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(ΙΙ) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.     

A storm event-based approach to TMDL development

It is vitally important to define the critical condition for a receiving water body in the total maximum daily load (TMDL) development process. One of the major disadvantages of using a continuous simulation approach is that there is no guarantee that the most critical condition will be covered within the subjectively selected representative hydrologic period, which is usually several years depending on the availability of data. Another limitation of the continuous simulation approach, compared to a design storm approach, is the lack of an estimate of the risk involved. Because of the above limitations, a storm event-based critical flow-storm (CFS) approach was previously developed to explicitly address the critical condition as a combination of a prescribed stream flow and a storm event of certain magnitude, both having a certain frequency of occurrence and when combined, would create a critical condition. The CFS approach was tested successfully in a TMDL study for Muddy Creek in Virginia. The present paper reports results of a comparative study on the applicability of the CFS approach in Taiwan. The Dy-yu creek watershed in northern Taiwan differs significantly from Muddy Creek in terms of climate, hydrology, terrain, and other characteristics. Results show that the critical condition for different watersheds might be also different, and that the CFS approach could clearly define that critical condition and should be considered as an alternative method for TMDL development to a continuous simulation approach.     

Bioaccumulation and the soil factors affecting the uptake of arsenic in earthworm, Eisenia fetida

To better understand arsenic (As) bioaccumulation, a soil invertebrate species was exposed to 17 field soils contaminated with arsenic due to mining activity. Earthworms (Eisenia fetida) were kept in the soils for 70 days under laboratory conditions, as body burden increased and failed to reach equilibrium in all soils. After 70 days of exposure, XANES spectra determined that As was biotransformed to a highly reduced form. Uptake kinetics for As was calculated using one compartment model. Stepwise multiple regression suggested that sorbed As in soils are bioaccessible, and uptake is governed by soil properties (iron oxide, sulfate, and dissolved organic carbon) that control As mobility in soils. As in soil solution are highly related to uptake rate except four soils which had relatively high chloride or phosphate. The results imply that uptake of As is through As interaction with soil characteristics as well as direct from the soil solution. Internal validation showed that empirically derived regression equations can be used for predicting As uptake as a function of soil properties within the range of soil properties in the data set.     

Biological Effects of Carbon Monoxide vs. Whole Emissions from Engine with Catalyst

The introduction of oxidizing catalytic converters in the exhaust system of automobiles has been found to be effective in reducing carbon monoxide, total hydrocarbons, and some other components of tailpipe emissions. The utilization of these converters, however, has also caused further oxidation of sulfur compounds producing an increased amount of sulfur trioxide (SO₃) which yields sulfuric acid and sulfates.¹ Studies on the biological effects of these sulfur compounds are in progress in our laboratory and preliminary findings are reported separately. This paper compares the biological effects of exposure to whole emissions from engines with and without converter and exposure to carbon monoxide alone.