A preliminary investigation of the efficacy of riparian fencing schemes for reducing contributions from eroding channel banks to the siltation of salmonid spawning gravels across the south west UK

The low productivity of salmonids in many river systems across the UK is testament to their intolerance of water quality perturbations including those associated with excessive sedimentation. Catchment and fishery managers concerned with combating such issues require reliable information on the key sources of the sediment problem to target management and on the efficacy of the mitigation options being implemented. In recognition of the latter requirement, a pre- and post-remediation sediment sourcing survey was used to examine the potential for using sediment tracing to assemble preliminary information on the efficacy of riparian fencing schemes for reducing sediment contributions from eroding channel banks to salmonid spawning gravels in the Rivers Camel, Fal, Lynher, Plym, Tamar and Tavy in the south west of the UK. Respective estimates of the overall mean proportion (±95% confidence limits) of the interstitial sediment input to salmonid spawning gravels originating from eroding channel banks during the pre- (1999–2000) and post-remediation (2008–2009) study periods were computed at 97 ± 1% vs. 69 ± 1%, 94 ± 1% vs. 91 ± 1%, 12 ± 1% vs. 10 ± 1%, 92 ± 1% vs. 34 ± 1%, 31 ± 1% vs. 16 ± 1% and 90 ± 1% vs. 66 ± 1%. Whilst the study demonstrates the potential utility of the fingerprinting approach for helping to assemble important information on the efficacy of bank fencing as a sediment source control measure at catchment scale, a number of limitations of the work and some suggestions for improving experimental design are discussed. Equivalent data are urgently required for many sediment mitigation options to help inform the development of water quality policy packages designed to protect aquatic ecosystems.     

Comparative metabolism of phenanthrene in the rat and guinea pig.

In the present study the biotransformation of phenanthrene in the rat and guinea pig was investigated. 14C-labelled phenanthrene was administered by gavage in corn oil to Sprague-Dawley rats (10 mg/kg b.w./day) and guinea pigs (10 mg/kg b.w./day). Urine and feces were separately collected for the determination of the radioactivity content, and pooled urine was used for the analysis of metabolites. Phenanthrene was metabolized by the rat and guinea pig to free hydroxylated phenanthrenes and their conjugates. The percentages of conjugates, expressed as the total urinary radioactivity, were 39% glucuronides, 24% sulfates and 18% cysteinylglycine for rats; and 39% glucuronides, 23% sulfates and 28% cysteinylglycine for guinea pigs. Enzymatic hydrolysis of glucuronides and sulfates resulted in the formation of free 1,2-, 3,4- and 9,10-dihydrodiols of phenanthrene and 1-, 2-, 3-, and 4-hydroxyphenanthrene in both species.     

Chlorfenvinphos Dermal Absorption in Rats: Histological and Ultrastructural Changes in the Skin and Internal Organs

We studied the effect of chlorfenvinphos dermal absorption on the morphological picture of blood, on the histological and fine structure of tail skin, and on the histological structure of internal organs (lungs, heart, liver, spleen, and kidney) of rats. This study was conducted on 25 white Wistar rats, the tail skin of which was—or was not—hydrated before exposure. Rat tails were soaked in 0.5% or 0.05% chlorfenvinphos for 1 hr day for 3 months. Evident tendencies for a decrease in the absolute level of leukocytes and for an increase in the absolute level of erythrocytes in all experimental animals were observed. Histopathological changes in the internal organs were mildly manifested in only a few rats, mainly as liver and pulmonary hyperaemia. Rat tail skin at the direct exposure site showed hyperceratosis, intensive desquamation, and compensatory hyperplasia.     

Temporal variability in physical speciation of metals during a winter rain-on-snow event

Particulate matter in urban rivers transports a significant fraction of pollutants, changes rapidly during storm events, and is difficult to characterize. In this study, the physical speciation of trace metals and organic C in an urban river and upstream headwaters site in Torrington, CT, were measured during a winter rain-on-snow event. In addition, a selective fractionation scheme, using membrane and tangential-flow ultrafiltration methods to separate suspended particulate matter into sand, silt, clay, and colloid fractions, was evaluated based on the appropriateness of the chosen size categories. During peak runoff at the urban river site, total-recoverable concentrations of the metals Cu and Pb increased 6- and 13-fold to 16.9 and 9.5 microg L(-1), respectively, compared with baseflow concentrations. Concentrations of Cu and Pb reached only 0.9 and 0.86 microg L(-1) at the headwaters site. For the measured storm event, the majority of metals were transported by the urban river in association with coarse silt (20-80 microm particle diam.) during peak runoff. During peak runoff at the urban site, organic C associated with the large colloid fraction (0.1-1.0 microm) increased from 5% (at baseflow) to 54% of the total C in transport, whereas dissolved organic C and that associated with smaller colloids decreased from 91.5% (at baseflow) to 41% of the total. Other elements that were monitored as part of the study were Na, K, Ca, Mg, Fe, Mn, Al, Cd, Cl-, NO3(-), and SO4(2-). The chosen fractionation scheme was useful to characterize pollutant transport during this event, but further testing should be undertaken to determine the most appropriate size range categories, and to ensure that the sizes measured are comparable to those used in other studies.     

Transformation of hydroxylated derivatives of 2,5-dichlorobiphenyl and 2,4,6-trichlorobiphenyl by Burkholderia xenovorans LB400

The polychlorinated biphenyl (PCB)-degrading bacterium, Burkholderia xenovorans LB400, was capable of transforming three hydroxylated derivatives of 2,5-dichlorobiphenyl (2,5-DCB) (2′-hydroxy- (2′-OH-), 3′-OH-, and 4′-OH-2,5-DCB) when biphenyl was used as the carbon source (i.e., biphenyl pathway-inducing condition), although only 2′-OH-2,5-DCB was transformed when the bacterium was growing on succinate (i.e., condition non-inductive of the biphenyl pathway). On the contrary, hydroyxlated derivatives of 2,4,6-trichlorobiphenyl (2,4,6-TCB) (2′-OH-, 3′-OH-, and 4′-OH-2,4,6-TCB) were not significantly transformed by B. xenovorans LB400, regardless of the carbon source used. Gene expression analyses showed a clear correlation between the transformation of OH-2,5-DCBs and expression of genes of the biphenyl pathway. The PCB metabolite, 2,5-dichlorobenzoic acid (2,5-DCBA), was produced following the transformation of OH-2,5-DCBs. 2,5-DCBA was not further transformed by B. xenovorans LB400. The present study is significant because it provides evidence that PCB-degrading bacteria are capable of transforming hydroxylated derivatives of PCBs, which are increasingly considered as a new class of environmental contaminants.     

Acetylcholinesterase in honey bees (Apis mellifera) exposed to neonicotinoids, atrazine and glyphosate: laboratory and field experiments

In Québec, as observed globally, abnormally high honey bee mortality rates have been reported recently. Several potential contributing factors have been identified, and exposure to pesticides is of increasing concern. In maize fields, foraging bees are exposed to residual concentrations of insecticides such as neonicotinoids used for seed coating. Highly toxic to bees, neonicotinoids are also reported to increase AChE activity in other invertebrates exposed to sub-lethal doses. The purpose of this study was therefore to test if the honey bee’s AChE activity could be altered by neonicotinoid compounds and to explore possible effects of other common products used in maize fields: atrazine and glyphosate. One week prior to pollen shedding, beehives were placed near three different field types: certified organically grown maize, conventionally grown maize or non-cultivated. At the same time, caged bees were exposed to increasing sub-lethal doses of neonicotinoid insecticides (imidacloprid and clothianidin) and herbicides (atrazine and glyphosate) under controlled conditions. While increased AChE activity was found in all fields after 2 weeks of exposure, bees close to conventional maize crops showed values higher than those in both organic maize fields and non-cultivated areas. In caged bees, AChE activity increased in response to neonicotinoids, and a slight decrease was observed by glyphosate. These results are discussed with regard to AChE activity as a potential biomarker of exposure for neonicotinoids.     

Causes and consequences of a tropical forest gold rush in the Guiana Shield, South America

Statistical and spatial analyses of both historical time series and remotely sensed data show a link between the spatial distribution and growth of gold production across the Guiana Shield in northeast Amazonia. Results indicate that an exponential rise in production across an expanding area is primarily a delayed response to the 1971-1978 market flotation of international gold prices. The subsequent 10-fold (2-fold) average nominal (real) price increase has provided a compelling economic incentive to mass exploitation of lower-grade gold deposits. The ground-based and remotely sensed distributions of mining activity are strongly attached to these deposits that dominate the region's gold geology. The presence of these gold-bearing formations in conservation and sustainable timber zones has sparked social conflict and environmental degradation across the region. Left unmanaged, more than a quarter-million square-kilometer area of tropical forest zoned for protection and sustainable management could ultimately be compromised by the price-driven boom in gold mining through poorly integrated resource use planning, lack of reclamation effort, and control of illegal operations. Serious public health issues propagated through the unregulated mining environment further erode the financial benefits achieved through gold extraction. This study demonstrates in part how international economic policies successfully stabilizing more conspicuous centers of the global economy can have unintended but profound environmental and social impacts on remote commodity frontiers.