Impact of synthetic pyrethroid-sheep dip on the indigenous microflora of animal slurries

The chemical constituents of sheep dip in the UK are currently changing from organophosphate-based to synthetic pyrethroid-based insecticides. As a result, changes are also being made to the methods of disposal of these chemicals in the environment, such that pyrethroid sheep dips must now be diluted in animal slurry or water. To date, there is a lack of quantitative information on the impact of the insecticide on the indigenous microflora of animal slurries. This paper investigated the impact of Bayticol (synthetic pyrethroid sheep dip) over a range of concentrations on selected populations of bacteria within animal slurry. It was found that, with increasing pesticide concentration, there was up to a four orders of magnitude increase in the numbers of faecal coliforms and pathogens, such as putative Salmonella spp. These findings have implications for the disposal of sheep dip-amended animal slurries to land from several aspects: (i) the longevity of putative pathogens in the field may require re-evaluation of the time required before the return of grazing livestock to a slurry-amended field; (ii) the potential for the transfer of pathogenic bacteria and faecal coliforms into human and animal foodchains, and (iii) the increased potential for faecal coliforms being washed into streams, rivers and coastal bathing waters.

Bound pesticide residues in soils: a review

This article is a review of the current state of knowledge regarding the formation and biological/environmental significance of bound pesticide residues in soils. We begin by defining various terms used in our discussions and identifying the types/classes of pesticides which may be added to soil and interact with it. We then consider various soil properties and aspects of land management which will influence the nature and degree of the soil-pesticide association and discuss the possible physical and chemical binding mechanisms. We then move on to consider the role of microorganisms and other forms of soil biota in bound residue formation and the bioavailability of soil-borne pesticide residues. The review ends with a consideration of the significance of bound pesticide residues.

Bioavailability of persistent organic pollutants in soils and sediments--a perspective on mechanisms, consequences and assessment

It has been observed that as soil-pollutant contact time increases, pollutant bioavailability and extractability decreases. This phenomenon has been termed 'ageing'. Decreased chemical extractability with increased soil-chemical contact time is evident where both 'harsh' techniques, e.g. dichloromethane Soxhlet extraction, and 'non-exhaustive' techniques, e.g. butanol shake extraction, have been used. It has also been observed that the amount of chemical extracted by these techniques varies considerably over time. Similarly, decreases in bioavailability with increased soil-pollutant contact time have been described in bacterial, earthworm and other organism studies. From these investigations, it has been shown that the fraction of pollutant determined to be bioavailable can vary between organisms. Thus, there is an immediate definition problem, what is bioavailability? Additionally, if bioavailability is to be assessed by a chemical means, which organisms should (or can) be mimicked by the extraction procedure? This review provides a background to the processes inherent to ageing, a discussion of its consequences on bioavailability and ends with some reflections on the appropriateness of chemical extraction techniques to mimic bioavailability

Impact of electrical cable insulating oil on the mineralisation of [1-(14)C]glucose in soil

Subsurface high voltage electric cables are commonly insulated using dodecylbenzene in combination with mineral oil. This work assessed the impact of increasing concentrations of cable insulating oil (0-10% dry weight) on soil microbial respiration as determined by mineralisation of [1-(14)C]glucose (11 microg C g(-1) soil). Acute impact was assessed from 0 days to 21 days, and chronic impact was assessed after 300 days. This study found that cable insulating oil increased respiratory activity of soil microflora. The extent of impact was found to depend on both oil concentration and the length of oil-soil contact time. Following acute exposure (21-days oil-soil contact time), it was found that oil concentrations up to 1% promoted a significant (P<0.05) increase in the extent of [1-(14)C]glucose mineralisation to (14)CO(2) relative to the control. In contrast, higher concentrations of cable insulating oil (5% and 10%) promoted no significant (P0.05) increase in the extent of [1-(14)C]glucose mineralisation to (14)CO(2) relative to the control. Following chronic exposure (300-days oil-soil contact time), the extent of mineralisation was greater at all oil concentrations applied relative to the control. For oil concentrations up to and including 1%, there was a decrease in the extent of elevation in mineralisation relative to the values after 21-days exposure. At higher oil concentrations, namely 5% and 10%, the extent of elevation in mineralisation was comparable with that after 21-days oil-soil contact time. We suggest that the increase in mineralisation of glucose indicates that cable insulating oil is a readily available carbon source to the carbon-limited soil microflora.

Methods for the analysis of PCBs in human food, faeces and serum

A method was developed to determine trace concentrations of a range of individual PCB congeners in biological samples (serum, food and faeces) using GC-MS, to prepare a mass balance of PCBs in humans. A simple method for the analysis of PCBs in human serum, which excluded an extraction step, was first employed. Results indicated that the recoveries of 13C12 PCB spikes were variable. A soxhlet extraction step was added and was found to be efficient and reproducible. A quality control routine and method validation results are presented. In batch tests of the methods presented it was found that the serum analysis method gave within batch mean 13C12 spike recoveries of 98-120% and standard deviations between 6 and 20%. The food/faeces analysis method gave within-batch mean 13C12 spike recoveries of 88-100%, and within batch standard deviations between 4 and 12%. The batch to batch mean recovery for serum analysis was 100%, with an RSD of 9% for high spikes and 10% for low spikes. For food/faeces analysis the batch to batch average recovery was 110%, with an RSD of 5% for high spikes and 9% for low spikes.

Feasibility of using prokaryote biosensors to assess acute toxicity of polycyclic aromatic hydrocarbons

The aim of this study was to assess the acute toxicity of polycyclic aromatic hydrocarbons using lux-marked bacterial biosensors. Standard solutions of phenanthrene, pyrene and benzo[a]pyrene were produced using 50 mM hydroxpropyl-beta-cyclodextrin solution which contained each respective polycyclic aromatic hydrocarbon at 6.25 times the aqueous solubility limit of the compound. The polycyclic aromatic hydrocarbon solutions were incubated with each of the biosensors for 280 min and the bioluminescence monitored every 20 min. Over the incubation time period, there was no significant decrease in bioluminescence in any of the biosensors tested with the exception of Rhizobium leguminosarum biovar trifolii TA1 luxAB. In this series of incubations, there was a dramatic increase in bioluminescence in the presence of phenanthrene (2.5 times) and benzo[a]pyrene (3 times) above that of the background control (biosensor without polycyclic aromatic hydrocarbon) after 20 min. Over the next 3 h, bioluminescence decreased to that of the control. An ATP assay was carried out on the biosensors to assess if uncoupling of the oxidative phosphorylation mechanisms in the respiratory chain of the cells had occurred. However, it was found that the polycyclic aromatic hydrocarbons had no effect on the organisms indicating that there was no uncoupling. Additionally, mineralisation studies using 14C-labelled polycyclic aromatic hydrocarbons showed that the biosensors could not mineralise the compounds. This study has shown that the three polycyclic aromatic hydrocarbons tested are not acutely toxic to the prokaryotic biosensors tested, although acute toxicity has been shown in other bioassays. These results question the rationale for using prokaryote biosensors to assess the toxicity of hydrophobic chemicals, such as polycyclic aromatic hydrocarbons.

Heterotrophic growth on phenolic mixtures by Ochromonas danica

Because phenols are one of the most common groups of organic pollutants in the aquatic environment, heterotrophic growth-linked biodegradation of phenol and its methylated homologues by the eukaryotic alga Ochromonas danica (CCAP 933/2B) was investigated. The alga grew heterotrophically on phenol and mixtures of phenol with o- or p-cresols, or with 2,5-, 2,6-, 3,4- or 3,5-xylenols as the sole sources of carbon in the dark at 25 degrees C. Commensurate with growth, the alga removed phenol, both cresol isomers and 2,5- and 3,4-xylenols from the growth media over the incubation periods. In every case, phenol was removed preferentially to the methylated cosubstrates, but the rates of removal for phenol were slower than in incubations where phenol was the sole carbon source.

Biodegradation of phenols by the alga Ochromonas danica

The eukaryotic alga Ochromonas danica, a nutritionally versatile, mixotrophic chrysophyte, grew on phenol as the sole carbon source in axenic culture and removed the phenol carbon from the growth medium. Respirometric studies confirmed that the enzymes involved in phenol catabolism were inducible and that the alga oxidized phenol; the amount of oxygen consumed per mole of oxidized substrate was approximately 65% of the theoretical value. [U-14C]phenol was completely mineralized, with 65% of the 14C label appearing as 14CO2, approximately 15% remaining in the aqueous medium, and the rest accounted for in the biomass. Analysis of the biomass showed that 14C label had been incorporated into the protein, nucleic acid, and lipid fractions; phenol carbon is thus unequivocally assimilated by the alga. Phenol-grown cultures of O. danica converted phenols to the corresponding catechols, which were further metabolized by the meta-cleavage pathway. This surprising result was rigorously confirmed by taking the working stock culture through a variety of procedures to check that it was axenic and repeating the experiments with algal extracts. This is, as far as is known, the first definitive identification of the meta-cleavage pathway for aromatic ring degradation in a eukaryotic alga, though its incidence in other eukaryotes has been (infrequently) suggested.

Metabolism of phenols by Ochromonas danica

This study investigated the catabolic potential of a eukaryotic alga to degrade one of the most common organic pollutants, phenol. The alga, Ochromonas danica (993/28), was selected for study after screening for its heterotrophic capabilities. The catabolic versatility of the alga was elucidated by incubating with a variety of phenolic compounds. The alga removed phenol, all the cresol isomers and 3,4-xylenol from its incubation media, with phenol being removed more rapidly than any of its methylated homologues. Consequently, the alga was found to have a greater specificity for phenol than for o- or p-cresols. This study shows that O. danica could catabolize phenol and its methylated homologues.