Hydrogen production by anaerobic microbial communities exposed to repeated heat treatments.

Biological hydrogen production by anaerobic mixed communities was studied in laboratory-scale bioreactors using sucrose as the substrate. A bioreactor in which a fraction of the return sludge was exposed to repeated heat treatments performed better than a control bioreactor without repeated heat treatment of return sludge and produced a yield of 2.15 moles of hydrogen per mole of sucrose, with 50% hydrogen in the biogas. Terminal restriction fragment length polymorphism analysis showed that two different Clostridium groups (comprised of one or more species) were dominant during hydrogen production. The relative abundance of two other non-Clostridium groups increased during periods of decreased hydrogen production. The first group consisted of Bifidobacterium thermophilum, and the second group included one or more of Bacillus, Melissococcus, Spirochaeta, and Spiroplasma spp.     

Post-copulatory guarding,female choice and the levels of gregarine infections in the field cricket,Gryllus bimaculatus

Summary A recent model in sexual selection has proposed a role for parasites in maintaining heritable fitness variation. Females are envisaged as benefitting from preferentially mating with males that show resistance to infection. The post-copulatory guarding behaviour characteristic of many species of field cricket, has been envisaged as a means by which females assess male health and vigour. This hypothesis was tested in a field cricket, G. bimaculatus, which harbours a protozoan gut parasite. In enclosed arena trials, no direct correlations between female behaviours and levels of infection in males were found. However, there were significant correlations between the intensity of male guarding and the number of parasites found in the gut; infected males guarded more intensely in order to maintain contact with the female. In a second experiment simulating open field conditions, females left heavily parasitized males sooner than mildly or uninfected individuals. These data are discussed in relation to female choice for male health and vigour.     

Triploidy: Pregnancy complications and clinical findings in seven cases

Seven cases of triploidy were encountered by the Prenatal Diagnosis Program at Dartmouth–Hitchcock Medical Center over an 8-year period through associated pregnancy complications. We describe the characteristic findings that facilitate prenatal diagnosis and management. Our experience includes fetuses with major central nervous system abnormalities (spina bifida aperta, holoprosencephaly) and anterior abdominal wall defects, which are detectable with routine prenatal diagnostic screening examinations (ultrasound and AFP). In addition, we stress the importance of recognizing obstetric complications and associated cystic placental changes, which are quite common among triploid conceptuses. Molar changes associated with triploidy have a more benign prognosis than that associated with diploid moles. Such molar changes may relate to the presence of a diploid paternal chromosome complement. The usefulness of cytofluorometric DNA determinations in helping to confirm a clinical suspicion of triploidy is emphasized. These cases are presented in an effort to facilitate prenatal recognition and management of this common cytogenetic condition and prevent unnecessary Caesarean section deliveries.     

Offensive and defensive sperm competition roles in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

Sperm competition is predicted to generate opposing selection pressures on males. On one hand, selection should favour ‘defensive’ adaptations that protect a male’s ejaculate from displacement, while, on the other hand, selection should favour ‘offensive’ adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm precedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male’s sperm precedence (both P ₁ and P ₂) was detected, and an individual’s defensive (P ₁) and offensive (P ₂) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for ‘defensive’ and ‘offensive’ adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male’s ability to be successful when mating in an ‘offensive’ and a ‘defensive’ role.     

The degradation of plastic litter in rivers: Implications for beaches

Polythene sheeting is a major litter component on estuarine beaches and river banks. Sanitary towel backing strips, which are one of the commonest items of sewage related debris found on beaches, enter the riverine system via combined sewer overflows. Investigations on these items, positioned at natural riverine stranding levels, showed that after an initial rapid breakdown little further loss of tensile strength occurred. Experiments carried out on backing strips, buried in the bank suspended from a tree and tethered to the bank, showed significant change. Buried samples retained the greatest tensile strength retention, dropping no lower than 90 %, the other samples showed similar retention rates at 80%. The difference is probably due to photodegradation as biodegradation effects were minimal. Probably, the longevity of such plastics is a major reason for their abundance and widespread distribution both on river banks and beaches.     

Elevated Levels of Cadmium and Zinc in Paddy Soils and Elevated Levels of Cadmium in Rice Grain Downstream of a Zinc Mineralized Area in Thailand: Implications for Public Health

Prolonged consumption of rice containing elevated cadmium (Cd) levels is a significant health issue particularly in subsistence communities that are dependent on rice produced on-farm. This situation is further exacerbated in areas of known non-ferrous mineralization adjacent to rice-based agricultural systems where the opportunity for contamination of rice and its eventual entry into the food chain is high. In the current study, an assessment of the degree of soil Cd and Zn contamination and associated rice grain Cd contamination downstream of an actively mined zone of Zn mineralization in western Thailand was undertaken. Total soil Cd and Zn concentrations in the rice-based agricultural system investigated ranged from 0.5 to 284 mg kg⁻¹ and 100 to 8036 mg kg⁻¹, respectively. Further, the results indicate that the contamination is associated with suspended sediment transported to fields via the irrigation supply. Consequently, the spatial distribution of Cd and Zn is directly related to a field’s proximity to primary outlets from in-field irrigation channels and inter-field irrigation flows with 60–100% of the Cd and Zn loading associated with the first three fields in irrigation sequence. Rice grain Cd concentrations in the 524 fields sampled, ranged from 0.05 to 7.7 mg kg⁻¹. Over 90% of the rice grain samples collected contained Cd at concentrations exceeding the Codex Committee on Food Additives and Contaminants (CCFAC) draft Maximum Permissible Level for rice grain of 0.2 mg Cd kg⁻¹. In addition, as a function of demographic group, estimated Weekly Intake (WI) values ranged from 20 to 82 μg Cd per kg Body. This poses a significant public health risk to local communities. The results of this study suggest that an irrigation sequence-based field classification technique in combination with strategic soil and rice grain sampling and the estimation of WI values via rice intake alone may be a useful decision support tool to rapidly evaluate potential public health risks in irrigated rice-based agricultural systems receiving Cd contaminated irrigation water. In addition, the proposed technique will facilitate the cost effective strategic targeting of detailed epidemiological studies thus focusing resources to specific ‘high risk’ areas.     

An experimental comparison of conservative versus optimal collision avoidance warning system thresholds

In the distributed signal detection theoretic (DSDT) model, the human operator and the warning mechanism are independent decision makers who work together as a team. The DSDT demonstrates that the optimal warning threshold, in general, differs from the signal detection theoretic (SDT) threshold, which assumes a single decision maker. This prediction was tested in an experiment where drivers received monetary rewards for making safe passing decisions on a driving simulator. The experiment focused on evaluating the quality of the decision making of the drivers, and not on perceptual issues. A collision avoidance system provided a warning when the probability of an inadequate overtaking gap exceeded a threshold. Three thresholds were tested. The control threshold resulted in no detections or false alarms. The DSDT threshold resulted in some misses but no false alarms. The SDT threshold resulted in no misses but frequent false alarms. As predicted, (1) drivers performed the best when the warning system used the DSDT threshold, and (2) use of the SDT threshold improved performance over the control threshold, even though four of the 10 drivers occasionally ignored the warning and made risky passing attempts in the SDT conditions, possibly because of earlier false alarms. These findings support the conclusion that the DSDT model is a useful, quantitative tool that should be used by warning designers.     

Cadmium-hazard mapping using a general linear regression model (Irr-Cad) for rapid risk assessment

Research undertaken over the last 40 years has identified the irrefutable relationship between the long-term consumption of cadmium (Cd)-contaminated rice and human Cd disease. In order to protect public health and livelihood security, the ability to accurately and rapidly determine spatial Cd contamination is of high priority. During 2001–2004, a General Linear Regression Model Irr-Cad was developed to predict the spatial distribution of soil Cd in a Cd/Zn co-contaminated cascading irrigated rice-based system in Mae Sot District, Tak Province, Thailand (Longitude E 98°59′–E 98°63′ and Latitude N 16°67′–16°66′). The results indicate that Irr-Cad accounted for 98% of the variance in mean Field Order total soil Cd. Preliminary validation indicated that Irr-Cad ‘predicted’ mean Field Order total soil Cd, was significantly (p < 0.001) correlated (R ² = 0.92) with ‘observed’ mean Field Order total soil Cd values. Field Order is determined by a given field's proximity to primary outlets from in-field irrigation channels and subsequent inter-field irrigation flows. This in turn determines Field Order in Irrigation Sequence (Field Order^IS). Mean Field Order total soil Cd represents the mean total soil Cd (aqua regia-digested) for a given Field Order^IS. In 2004–2005, Irr-Cad was utilized to evaluate the spatial distribution of total soil Cd in a ‘high-risk’ area of Mae Sot District. Secondary validation on six randomly selected field groups verified that Irr-Cad predicted mean Field Order total soil Cd and was significantly (p < 0.001) correlated with the observed mean Field Order total soil Cd with R ² values ranging from 0.89 to 0.97. The practical applicability of Irr-Cad is in its minimal input requirements, namely the classification of fields in terms of Field Order^IS, strategic sampling of all primary fields and laboratory based determination of total soil Cd (T-Cd_P) and the use of a weighed coefficient for Cd (Coeff_W). The use of primary fields as the basis for Irr-Cad is also an important practical consideration due to their inherent ease of identification and vital role in the classification of fields in terms of Field Order^IS. The inclusion of mean field order soil pH (1:5_water) to the Irr-Cad model accounted for over 79% of the variation in mean Field Order bio-available (DTPA (diethylenetriaminepentaacetic acid)-extractable) soil Cd. Rice is the staple food of countries of the Greater Mekong Sub-region (includes Vietnam, Myanmar, Lao PDR, Thailand and Yunnan Province, China). These countries also have actively and historically mined Zn, Pb, and Cu deposits where Cd is likely to be a potential hazard if un-controlled discharge/runoff enters areas of rice cultivation. As such, it is envisaged that the Irr-Cad model could be applied for Cd hazard assessment and effectively form the basis of intervention options and policy decisions to protect public health, livelihoods, and export security.     

The effects of sewage on alpine streams in Kosciusko National Park,NSW

The impact of resort developments in three alpine streams of Kosciusko National Park was examined by the State Pollution Control Commission of NSW over 1981 and 1982. Physico-chemical measurements such as nutrient concentrations, stream flow and temperature were correlated with measures of periphyton growth using artificial substrates and the Thomas (1978) method for estimation of in-stream biomass.Stream flow was the major physical parameter controlling in-stream periphyton growth, far outweighing seasonal temperature variations. Nutrients emanating from resort developments were also a major influence on biomass and taxa. Natural accumulations occurred upstream of resort developments under low flow conditions and were associated with taxa typical of clean water conditions. The relationships between periphyton biomass and nutrient loads could be quantified.