Evaluation of effects of exposure time on aquatic toxicity with zooplanktons using a reduced life expectancy model

Traditionally in toxicological studies time is not studied as quantifiable variable but as a fixed endpoint. The Reduced Life Expectancy (RLE) model which relates exposure time and exposure concentration with lethal toxic effects was tested previously using fish data. In this current paper the effects of exposure time on aquatic toxicity with zooplanktons and various toxicants were evaluated using the RLE model based on ambient exposure concentration. The model was evaluated by plotting ln LT₅₀ against LC₅₀ using toxicity data with zooplanktons from the literature for metal, metalloid and organic compounds. Most of the experimental data sets can be satisfactorily correlated by use of the RLE model, but deviations occurred for some data sets. Those data sets were satisfactorily fitted by a two stage RLE model. This model was based on two phases: one in the peripheral system and other in the central system. Both the single and two stage RLE model support the hypothesis that toxicity is time dependent and decreases in a systematic way with increasing exposure time. A calculated normal life expectancy (NLT) can be obtained from the single stage model and is in accord with reported NLT but those obtained from the two stage RLE model are in excellent agreement.     

In vitro methane removal by volcanic pumice soil biofilter columns over one year

Soil methane (CH(4)) biofilters, containing CH(4)-oxidizing bacteria (methanotrophs), are a promising technology for mitigating greenhouse gas emissions. However, little is known about long-term biofilter performance. In this study, volcanic pumice topsoils (0-10 cm) and subsoils (10-50 cm) were tested for their ability to oxidize a range of CH(4) fluxes over 1 yr. The soils were sampled from an 8-yr-old and a 2-yr-old grassed landfill cover and from a nearby undisturbed pasture away from the influence of CH(4) generated by the decomposing refuse. Methane was passed through the soils in laboratory chambers with fluxes ranging from 0.5 g to 24 g CH(4) m(-3) h(-1). All topsoils efficiently oxidized CH(4). The undisturbed pasture topsoil exhibited the highest removal efficiency (24 g CH(4) m(-3) h(-1)), indicating rapid activation of the methanotroph population to the high CH(4) fluxes. The subsoils were less efficient at oxidizing CH(4) than the topsoils, achieving a maximum rate oxidation rate of 7 g CH(4) m(-3) h(-1). The topsoils exhibited higher porosities; moisture contents; surface areas; and total C, N, and available-P concentrations than the subsoils, suggesting that these characteristics strongly influence growth and activity of the CH(4)-oxidizing bacteria. Soil pH values and available-P levels gradually declined during the trial, indicating a need to monitor chemical parameters closely so that adjustments can be made when necessary. However, other key soil physicochemical parameters (moisture, total C, total N) increased over the course of the trial. This study showed that the selected topsoils were capable of continually sustaining high CH(4) removal rates over 1 yr, which is encouraging for the development of biofilters as a low-maintenance greenhouse gas mitigation technology.     

The changing sediment load of the Mekong River

The sediment loads of many of the world's major rivers have changed significantly in recent years due to land-use change, reservoir construction, and other human impacts on their drainage basins. For many rivers, the loads have decreased, whereas for others, they have increased. Such changes can have important implications for both the natural functioning of the system as well as for human exploitation of the river system. This paper considers the evidence for recent changes in the sediment load of the Mekong River. The available data have a number of limitations in terms of both sampling frequency and the period of coverage, but they have been processed to provide a basis for considering the changes in the sediment load of the river over the period extending from the early 1960s to 2002. Although there is evidence of increasing loads at some measuring stations, the overall trends show little evidence of major changes, and the system provides evidence of buffering through storage. As of 2002, the construction of major dams on the headwaters in China appears to have had little impact on the sediment load, although as further larger dams are commissioned, the sediment load of the Mekong can be expected to decrease.     

Prediction of bioconcentration factors under non-equilibrium conditions

With the bioconcentration of lipophilic compounds by aquatic organisms when equilibrium between water and biota is attained, the logarithm of the bioconcentration factor has a direct linear relationship with the logarithm of the octanol/water partition coefficient. In practice, however, equilibrium may not be reached, particularly for more lipophilic compounds. It is shown theoretically, and confirmed by use of published experimental results on fish, that a different direct linear relationship also exists between the logarithms of the bioconcentration factor and the partition coefficient for compounds not achieving equilibrium after a specific exposure time. Thus, non-equilibrium bioconcentration factors can be predicted from their partition coefficients. The constants in the non-equilibrium linear equation are related to those from the relationships between equilibrium bioconcentration factors and the partition coefficients, and between the first-order clearance rate constants and the partition coefficients.     

Maternal alphafetoproteln screening by the polypropylene tube immunoradiometric assay on dried blood

The polypropylene tube immunoradiometric assay for alphafetoprotein (AFP) determination was applied to maternal serum along with a radioimmunoassay technique during the second trimester of pregnancy. Blood from pregnant women was collected by finger prick on strips of chromatography paper (Schleicher and Schuell No. 903C) and air dried. A 4·75 mm disc spot was eluted in anti-AFP coated tubes containing 1·0 ml of assay medium. After one hour the medium was vortexed and the tubes washed and counted on a Concept 4^tm (Micro- medic Systems, Horsham, PA.19044). The sensitivity of the technique is about 9 μg/l (35 ng/l in the assay) by the Rodbard formula. The concordance between the dried blood and the serum RIA tests in normal pregnancies was over 90 per cent at the 95th and 97th percentiles. This assay on dried blood spotted on chromatography paper was tested on 1003 patients and proved to be an ideal alternative to whole serum screening techniques: it minimizes sample manipulations and can easily be integrated into an existing newborn screening programme.     

Temporal variations in turbidity in an oil sands pit lake

Environmental Fluid Mechanics - We investigated temporal variations in turbidity in Base Mine Lake, an oil sands pit lake, located in northeast Alberta, Canada. The lake has a surface area of...     

Role of secondary metabolites and pigments in the epidermal tissues, ripe ovaries, viscera, gut contents and diet of the sea cucumber Holothuria atra

The epidermal tissues, ovaries, viscera, gut contents, and the diet of Holothuria atra (Jaeger), collected from the Great Barrier Reef (GBR), Australia, just prior to spawning, contained carotenoid pigments, mycosporine-like amino acids (MAAs) and three other metabolites in varying proportions. Mycosporine-glycine (mycosporine-gly), palythine, asterina-330, shinorine, mycosporine-2-gly, porphyra-334, and palythinol were present in the epidermal tissues. Mycosporine-gly was the major MAA in the epidermal tissues, gut contents and the diet, and the only MAA present in the ripe ovaries and the viscera. Gadusol, a metabolite with antioxidant properties, which co-occurs with MAAs, and in certain instances with trace amounts of 6-deoxygadusol in unfertilised and fertilised eggs and developing larvae of some marine invertebrates and vertebrates, was absent from H. atra. However, 6-deoxygadusol, with similar physical and chemical properties to gadusol, and the proposed biosynthetic precursor of MAAs, was present, but only in the ovaries. This is first report of the presence of this proposed biogenetic precursor of MAAs in significant amounts in a marine invertebrate. Approximately 90% of the total carotenoids of the epidermal tissues, ovaries and viscera of H. atra are highly oxidised, the main component being astaxanthin followed by canthaxanthin. These were the major carotenoids present in the ovaries and the total carotenoid content was highest in the ovaries. β-carotene, a common egg carotenoid, was present in trace quantities in the ovaries but, along with the xanthophylls lutein and zeaxanthin, it occurred in significant amounts in the gut contents and the diet of H. atra. Carotenoid patterns in the epidermal tissues and viscera were strikingly similar, containing β-carotene, canthaxanthin, astaxanthin, zeaxanthin, lutein, phoenicoxanthin and echinenone. The alkaloids homarine and isomeric trigonelline, (structurally unrelated to MAAs) and 6-deoxygadusol were present only in the ovaries and the viscera. It is suggested that these metabolites and pigments are either involved with photoprotection or reproduction, or associated with both processes. The origin, biogenetic relationships and the roles of these metabolites and pigments in H. atra are discussed. Received: 21 November 1997 / Accepted: 14 September 1998     

Relationships between partition coefficient,uptake rate constant,clearance rate constant and time to equilibrium for bioaccumulation

Theoretical derivations together with published experimental data on bioaccumulation of lipophilic compounds by certain groups of fish indicates that the uptake and clearance rate constants have a fixed relationship to the octanol to water partition coefficient over the partition coefficient range 10^2.5 to 10⁶. This allows the calculation of times to establish effective equilibrium, and significant bioaccumulation of compounds in relation to the partition coefficient. By extrapolation superlipophilic compounds (partition coefficients > 10⁶) have been shown to require a minimum period of 0.5 years increasing to 10 years when P = 10⁸ to establish effective equilibrium and compounds with partition coefficients >10¹³ are not bioaccumulated to any significant extent. In practice then, a direct relationship between the bioaccumulation factor and the partition coefficient will not result with superlipophilic componds.     

Critical evaluation of the measurement of the 1- octanol / water partition coefficient of hydrophobic compounds

Data on the experimental measurement of the octanol/water partition coefficient (K_ow) with hydrophobic compounds was assembled from the literature. The precision, characterised by the standard deviation of mean K_ow values based on five commonly used experimental methods, over an extended K_ow range was found to generally decline with compounds having log K_ow > 5.5. In the log K_ow range from 2.0 to 5.5 there was little difference between the mean values of log K_ow determined by the different methods but major differences occured with compounds having log K_ow > 5.5. The agreement between calculated ClogP values and K_ow values derived from individual experimental methods indicated that ClogP overestimates log K_ow from all experimental methods with compounds having values greater than 5.5.