An investigation of adsorption at the air-water and soil-water interfaces for non-micellizing ethylene oxide-propylene oxide surfactants

Adsorption at the air–water interface and soil sorption from aqueous solution have been investigated for a group of ethylene oxide (EO)–propylene oxide (PO) block copolymeric surfactants. The group which have a common structural formula of EO_m PO_n EO_m is distinguished by the fact that they have large critical micelle concentration (CMC) values and therefore do not readily form micelles at common environmental concentrations and temperatures. Adsorption at the air–water interface is readily shown to be driven by the size of the hydrophobic PO block. The size of the reduction in surface tension produced by a common concentration of 10⁻⁵ mol dm⁻³ linearly increases with the size of the PO block as does the efficiency of adsorption at the air–water interface as measured by pC₂₀ – the negative logarithm of the surfactant concentration that produces a reduction in surface tension of 20 mN m⁻¹. Soil sorption data have also been captured for these compounds and the data are readily fitted to the Freundlich adsorption isotherm. However soil sorption is shown to be inversely related to the molecular mass of the molecules and appears to be related to the size of the hydrophilic EO blocks in the molecule.     

The predicted environmental distribution of some PCB replacements

Physical and chemical properties which control the environmental distribution of five PCB replacement chemicals (di-isopropylnaphthalenes, phenylxylylethanes, butylated monochlorodiphenyl ethers, isopropylbiphenyls and tetrachloroethylene) have been obtained. These data are used to predict the distribution of these chemicals, a pentachlorobiphenyl and $\text{p,p′}$-DDE in an evaluative environment using a fugacity approach. This simple model gives no information about reactivity or persistence. More complex fugacity models are used to compare these additional features of a di-isopropylnaphthalene PCB replacement with those of a PCB.     

城市土壤中重金属元素的积累及其微生物效应

与农村土壤相比,阿伯丁市城市土壤(路边土、公园土)的微生物特征发生了显著的改变,微生物基底呼吸作用明显增强,但微生物生物量却显著降低,微生物生理生态参数C_mic/C_org、q_co2值明显升高,Biolog数据显示城市土壤对能源碳的消耗量和速度显著升高.对重金属元素研究表明,与农村土相比城市土壤中重金属Pb、Zn、Cu、Ni已经有明显积累,化学形态研究表明Pb主要与氧化铁有关,Ni、Zn以残渣态为主,Cd以有效态为主,而Cu除有效态外,其它结合形态基本具有同等重要的意义.主成分分析表明,有效态Pb是控制城市土壤与农村土壤微生物特征差异的主要因素,其次为Zn,Cu和Ni的有效态和有机态亦有一定的作用效应.     

Dietary constraints on reproductive periodicity in two sympatric deep-sea astropectinid seastars

Examination of the diet of two sympatric species of seastar, Bathybiaster vexillifer and Plutonaster bifrons from 2200 m depth in the Rockall Trough, NE Atlantic Ocean (57°18'N; 10°28'W), suggested that diet may determine the different reproductive patterns found between these two species. In the non-seasonally breeding B. vexillifier, the diet showed a high Shannon-Wiener prey diversity index, the dominant prey being the irregular echinoid Hemiaster expergitus together with a variety of prosobranch gastropods and protobranch bivalves. By contrast, the prey diversity in the seasonally breeding P. bifrons was significantly lower than that of B. vexillifer. In addition, organic carbon content in the sediment residue in the stomachs of P. bifrons displayed a seasonal cycle, while no such seasonality was detected in B. vexillifer. The stomachs of P. bifrons also contained a higher proportion of scavenged material, including the seasonally available remains of mesopelagic blue whiting. These data, together with Bathysnap (time-lapse camera) observations of feeding behaviour in both species, suggest that B. vexillifer is a predator feeding deep in the sediment, whereas P. bifrons feeds close to the sediment surface where it is affected by the seasonal availability of phytodetritus and fish carcasses.     

Fugacity models of indoor exposure to volatile chemicals

A method of calculating the atmospheric concentration of a volatile chemical in confined volumes is presented and illustrated which uses the fugacity concept to simplify the manipulation of the various transport and reaction terms. The method is particularly suitable for estimating exposure to chemicals which may be released by evaporation into a house, work place, or partially confined outdoor environment in which there are several volumes (eg. rooms) with known ventilation characteristics. Illustrative calculations are presented.     

The impact of climate change on the soil/moisture regime of Scottish mineral soils

The likely impact of climate change on the moisture regime of Scottish soils and consequently on agriculture and land use has been addressed using a novel Geographic Information Systems (GIS) approach. Current estimates of changes in summer precipitation by the year 2030 are 0% with an associated uncertainty of +/- 11%. This study considers the worst case scenario of a decrease in rainfall by 11% which will lead to some low rainfall areas experiencing an increased drought risk, particularly on lighter soils. Wet areas with heavy soils could benefit from an increase in the accessibility period for machinery. As the major agricultural land in Scotland is located on the relatively dry east coast where localised problems due to drought are not uncommon even under the present climate, the detrimental effects of a decrease in rainfall for the whole of Scotland are therefore likely to outweigh the benefits. Approximately 8% of Scotland has been identified in this study as soil/climate combinations which will be susceptible to drought should summer rainfall decrease by 11% and summer temperature increase by 1.4 degrees C.     

Costs and benefits of urban erosion and sediment control: The North Carolina experience

The EPA’s new nonpoint source pollution control requirements will soon institutionalize urban erosion and sediment pollution control practices nationwide. The public and private sector costs and social benefits associated with North Carolina’s program (one of the strongest programs in the country in terms of implementation authority, staffing levels, and comprehensiveness of coverage) are examined to provide general policy guidance on questions relating to the likely burden the new best management practices will have on the development industry, the likely costs and benefits of such a program, and the feasibility of running a program on a cost recovery basis. We found that urban erosion and sediment control requirements were not particularly burdensome to the development industry (adding about 4% on average to development costs). Public-sector program costs ranged between $2.4 and $4.8 million in fiscal year 1989. Our contingent valuation survey suggests that urban households in North Carolina are willing to pay somewhere between $7.1 and $14.2 million a year to maintain current levels of sediment pollution control. Our benefit-cost analysis suggests that the overall ratio is likely to be positive, although a definitive figure is elusive. Lastly, we found that several North Carolina localities have cost recovery fee systems that are at least partially self-financing. This article is based on research by the authors for the North Carolina Department of Environment, Health and Natural Resources (DEHNR). The views are those of the research team and do not necessarily reflect the position of DEHNR.