Alan Dowding

Investigation into the formation of PAHs in foods prepared in the home to determine the effects of frying, grilling, barbecuing, toasting and roasting

The effects of frying, grilling, barbecuing, toasting and roasting on the formation of 27 different PAHs in foods were investigated. A total of 256 samples from in-house cooking experiments were produced. There was little evidence of PAH formation during the grilling, frying, roasting and toasting experiments. Comparison with the raw materials used in the experiments showed little or no increase in PAH concentrations for all of the sample types, regardless of distances from the heat source, cooking mediums and intensity of cooking conditions. Barbecuing with charcoal plus wood chips however resulted in the formation of benzo[a]pyrene in most foods; for beef burgers only, barbecuing over charcoal (without the use of wood chips) gave the highest levels. In general PAH levels increased when the food was barbequed closer to the heat source. For sausages cooked over briquettes, and for beef burgers, beef and salmon cooked over charcoal, the concentration of PAHs was lower when the food was closer to the heat source. Cooking time may result in a moderate increase of PAHs in some foods, although concentrations in beef burgers appeared to fall when cooking time was extended by 50-100%.

The assimilation of dioxins and PCBs in conventionally reared farm animals: Occurrence and biotransfer factors

The assimilation of PCDD/Fs and PCBs in chickens, pigs and sheep was investigated in studies using conventional animal husbandry practices. Closely matched samples of muscle (meat), liver, kidneys, eggs, milk, feed, soil and grass were collected of which 105 were analysed. The data obtained were consistent with the PCB and PCDD/F TEQ concentrations to be expected in rural background locations. A slight decline in TEQ values in meat with increasing age was evident in pigs, sheep and broiler chickens. Higher TEQ values in meat from outdoor pigs compared to those raised indoors, and an increase in TEQs in eggs as a result of free-range conditions might be attributable to additional contaminant intakes from soil. TEQ values in samples of sheep meat were slightly higher than those for pigs and chickens and market ready lowland sheep showed higher meat TEQs than the highland species. PCDD/F TEQs were considerably higher in the liver than meat. Contaminant transfer from dietary sources was investigated using biotransfer factors (BTFs) which tended to be higher in chickens than in sheep or pigs. BTFs for all animals declined in magnitude with age, but on average, BTFs for pigs and chickens showed a sharper initial decline than for sheep. The relative magnitude of the BTFs usually followed the order: (highest first) PCB 153, PCB 169, PCB 126, 1,2,3,7,8-PeCDD/2,3,4,7,8-PeCDF and 2,3,7,8-TCDD. This may suggest that higher chlorinated congeners accumulate more readily in meat tissues. Congener-specific BTF variations were found to be associated with variables such as dietary composition during rearing, differences between feed and animal species.

The effects of flooding on dioxin and PCB levels in food produced on industrial river catchments.

This research examined the effect of regular flooding upon PCDD/F and PCB levels in milk, beef and lamb, produced on the floodplains of industrial river catchments. Our unique dataset included more than 200 samples analysed for PCDD/Fs and PCBs over two data collection phases (1998-1999 & 2008-2010) from working farms. A robust paired study design was adopted with samples taken from flood-prone farms and nearby control farms not subject to flooding. On industrial river catchments regular flooding is associated with higher PCDD/F and PCB levels in soils and grass. This contamination may be transferred to food but the impact varied by food type. These contrasts may be due to physiological differences between animals, the ages at which they are sent to market and differences in animal husbandry. To minimise the risks of producing food on flood-prone land in industrial river catchments, as well as on any land with elevated PCDD/F and PCB levels, this research suggests a number of options. The choice of livestock may be important and as an example in our study beef cattle accumulated PCDD/Fs to a higher degree than sheep. Land management may also play a role and could include minimising the time that livestock spend on such land or feeding commercial feed, low in PCDD/Fs and PCBs, where appropriate.

The effects of river flooding on dioxin and PCBs in beef

In 2008-2010, samples of meat from 40 beef cattle, along with grass, soil and commercial feed, taken from ten matched pairs of flood-prone and control farms, were analysed for PCDD/Fs and PCBs. Concentrations were higher in soil and grass from flood-prone farms. The beef samples from flood-prone farms had total TEQ levels about 20% higher than on control farms. A majority of flood-prone farms (7/10) had higher median levels in beef than on the corresponding control farm. This first controlled investigation into PCDD/F and PCB contamination in beef produced on flood-prone land, presents robust evidence that flooding is a contaminant transfer mechanism to cattle raised on river catchments with a history of urbanisation and industrialisation. PCDD/F and PCB sources in these river systems are likely to be a result of the legacy of contamination from previous industrialisation, as well as more recent combustion activity or pollution events.

Transfer and uptake of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) into meat and organs of indoor and outdoor reared pigs

This study was designed to investigate how and to what extent PCDD/Fs and PCBs are transmitted from exposure sources to porcine muscle and other tissues derived from pigs. The experimental approach involved two longitudinal studies in which indoor and outdoor pigs were reared to market readiness using typical animal husbandry practices; closely matched samples of soil, feed, bedding, meat, etc. were collected and analysed for PCDD/Fs and PCBs. The total PCDD/F + PCB WHO-TEQs in pig liver were much higher than in meat and kidney samples from the same animals and exceeded the current relevant European Union maximum limits (6 ng PCDD/F-TEQ kg−1 fat). Liver samples were also characterised by much lower PCB contributions to the total TEQ than for the corresponding meat and kidney samples, and by a predominance of many of the hepta- and octa-substituted PCDD/Fs. At ages approaching market readiness, TEQ values in meat samples from outdoor pigs tended to be slightly higher than those from comparable ages in the indoor programme, possibly due to additional intake from soil. Biotransfer factors (BTFs) were derived for each of the 39 PCDD/F and PCB congeners measured. Interpretation of the findings focused particularly on trends in four selected congeners, namely: 2,3,7,8-TCDD, 2,3,4,7,8-PeCDF, PCB 153 and PCB 169. Increases in the BTF for PCB 169 in the pig-rearing programmes were noticed when the diet changed from being dominated by sows milk to feed. Much higher transfer factors for many of the more heavily chlorinated PCDD/Fs (e.g. 2,3,4,7,8-PeCDF) were found in liver compared with meat or kidney samples from the same animals. Soil consistently accounted for at least 30% of input for many hexa- or higher chlorinated PCDD/Fs, while it rarely representing more than 10% of the total intake.

Dioxins and polychlorinated biphenyls (PCDD/Fs and PCBs) in food from farms close to foot and mouth disease animal pyres

To control the outbreak of foot and mouth disease, which occurred in the UK in early 2001, a large number of farm animals were slaughtered. Where it was not possible to render or landfill the carcasses, they were destroyed by burning on open pyres, with wood, coal and other materials. Uncontrolled combustion such as this is known to produce small quantities of dioxins and an investigation was made into whether, as a result of the burning, there was an elevation in the concentrations of these compounds in food produced in the areas close to the pyres. With few exceptions, concentrations of PCDD/Fs and PCBs were within the expected ranges as predicted by reference data. No accumulation over time was evident from a repeat milk sampling exercise. Where elevated concentrations of PCDD/Fs and PCBs were found in chickens and eggs, they were in samples not destined for the food chain. Elevated levels in some samples of milk from Dumfries and Galloway were not found in earlier or later samples and may have been found as a result of a temporary feeding regime. Elevated concentrations in lamb from Carmarthenshire were from very young animals which would not have entered the food chain. There was no evidence of any significant increase in dietary exposure to PCDD/Fs and PCBs as a result of the FMD pyres.