The bactericidal effect of dendritic copper microparticles, contained in an alginate matrix, on Escherichia coli

Although the bactericidal effect of copper has been known for centuries, there is a current resurgence of interest in the use of this element as an antimicrobial agent. During this study the use of dendritic copper microparticles embedded in an alginate matrix as a rapid method for the deactivation of Escherichia coli ATCC 11775 was investigated. The copper/alginate produced a decrease in the minimum inhibitory concentration from free copper powder dispersed in the media from 0.25 to 0.065 mg/ml. Beads loaded with 4% Cu deactivated 99.97% of bacteria after 90 minutes, compared to a 44.2% reduction in viability in the equivalent free copper powder treatment. There was no observed loss in the efficacy of this method with increasing bacterial loading up to 10(6) cells/ml, however only 88.2% of E. coli were deactivated after 90 minutes at a loading of 10(8) cells/ml. The efficacy of this method was highly dependent on the oxygen content of the media, with a 4.01% increase in viable bacteria observed under anoxic conditions compared to a >99% reduction in bacterial viability in oxygen tensions above 50% of saturation. Scanning electron micrographs (SEM) of the beads indicated that the dendritic copper particles sit as discrete clusters within a layered alginate matrix, and that the external surface of the beads has a scale-like appearance with dendritic copper particles extruding. E. coli cells visualised using SEM indicated a loss of cellular integrity upon Cu bead treatment with obvious visible blebbing. This study indicates the use of microscale dendritic particles of Cu embedded in an alginate matrix to effectively deactivate E. coli cells and opens the possibility of their application within effective water treatment processes, especially in high particulate waste streams where conventional methods, such as UV treatment or chlorination, are ineffective or inappropriate.

Viability of calanoid copepod eggs from intertidal sediments: A comparison of three estuaries

Calanoid copepod nauplii hatched from intertidal sediment samples from 3 British estuaries, the Exe, the Humber and the Mersey. The Exe Estuary is exposed to low levels of urban and agricultural pollution but the Humber and Mersey are subject to more extensive urban and industrial pollution. Samples were taken from the Humber and the Exe in April and November 1995 and from the Mersey and the Exe in June and October 1995. The concentrations of polycyclic aromatic hydrocarbons (PAH) in the sediments were measured as an index of pollution. The PAH concentrations in sediment were lowest in the Exe (mean <100 mu g/g dry weight) with most values >200 mu g/g dry weight in the Humber and some >300 mu g/g dry weight in the Mersey. Many more nauplii hatched from incubated sediments from the Exe than from the more polluted estuaries in April, June and November but larger numbers of nauplii hatched from the samples from the Mersey than from the Exe in October. Eggs were extracted from the samples taken in October and November and incubated; 92% of those from the Exe, 48% of those from the Humber and 14% of those from the Mersey hatched. This is consistent with reduction in viability of eggs with increased pollution. The viability of copepod eggs from sediments appears to have potential as a technique for in situ bioassay of fine sediments.

Digestion of copepod eggs by larval turbot Scophthalmus maximus and egg viability following gut passage

Between 20.5 and 93.6 % of the subitaneous eggs of 6 species of egg-carrying copepods passed undigested through the digestive tracts of larval and early postlarval turbot Scophthalmus maximus. Viability of the eggs of Eurytemora affinis, E. velox and Euterpina acutifrons remained high on egestion (67.0 to 91.7 %), Pseudocalanus elongatus and Oncaea venusta eggs had low viability (1.1 to 1.5 %), while all Corycaeus anglicus eggs were rendered inviable. The indigestibility of the eggs denies the turbot larvae a potentially valuable food resource, while retention of high egg viability in certain species reduces the effect of predation.

The effect of pollution of intertidal sediments on the viability of calanoid copepod eggs

Calanoid copepod eggs have been extracted from intertidal sediments and hatched in the laboratory. Although most of the eggs which hatched did so within < 7 days, the hatching of some continued over a more prolonged period (> 20 days). This indicates that there were a significant number of diapausing or delayed hatching eggs. The species of calanoids present include some of which are known to produce diapausing eggs. Hatching of nauplii from incubated sediment samples was slower than from the extracted eggs indicating dormancy induced by the effects of burial in the sediment. Viability of the eggs has been related to chronic industrial or urban pollution as indicated by polycyclic aromatic hydrocarbon levels. These hatchings were conducted simultaneously with those for cleaner locations. The viability of eggs was significantly depressed in the more heavily polluted sites. An oil spill arising from the grounding of the "Sea Empress" at Milford Haven, UK, in February 1996 has provided a comparison of the impact of an acute situation with these chronic effects. An immediate drastic reduction in viability was followed by a recovery in the year following the spill. The data have provided no evidence for differences in the response to pollution between diapausing and subitaneous eggs.