The effects of river flooding on dioxin and PCBs in beef
Graphical abstract
Introduction
Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs, collectively referred to as “dioxins”), and polychlorinated biphenyls (PCBs) are widely recognised environmental and food contaminants. Historically, PCBs were widely used as cooling and insulating fluids for industrial transformers and capacitors while PCDD/Fs have never been produced intentionally and are formed as a by-product of combustion activities or in the production of organo-chlorine chemicals (Schecter and Gasiewicz, 2003). Their ubiquitous presence has caused concern due to their environmental persistence, their bioaccumulation potential, and their toxic properties. The health effects associated with these compounds include immunotoxicity, carcinogenicity, and reproductive and developmental effects (Schecter and Gasiewicz, 2003).
In developed countries, the occurrence of PCDD/Fs and PCBs is primarily a legacy of inadequate controls on emissions from sources of combustion, particularly waste incineration, and the historical use of PCBs. As PCBs have now been phased out, and industrial combustion emissions are tightly regulated, levels in the environment (Alcock and Jones, 1996, Schuster et al., 2011), food (Durand et al., 2008, Harrison et al., 1998) and humans (Alivernini et al., 2011, Lignell et al., 2009) are in decline. There is consequently a historical legacy of contamination due to the environmental persistence (half-lives measured in decades) of many of these compounds. In less developed countries, the situation is different, with rapid industrialisation leading to increasing emissions which are only now starting to be controlled (Zhao et al., 2011). Studies have indicated that in some of these countries, PCDD/F and PCBs levels in human tissue are now similar to those in European populations (Shen et al., 2009). There is also evidence that in these less developed countries, concentrations of PCDD/Fs and PCBs are still rising in humans (Sun et al., 2011).
To protect public health in all countries, it is essential to understand the mechanisms through which PCDD/F and PCBs in the environment can transfer to humans. The major route of transfer for most of the population where there is no history of occupational exposure, is through food, which is estimated to account for around 90% of body burden (Liem et al., 2000). This is due to the propensity of PCDD/Fs and PCBs to bioaccumulate in fatty foods such as fish, meat, dairy products, and eggs (Schecter and Gasiewicz, 2003). These foods have thus been shown to be major contributors to dietary intake (Fernandes et al., 2004, Food Standards Agency, 2003, Startin and Rose, 2003). PCDD/Fs and PCBs can contaminate foodstuffs through several pathways, especially atmospheric deposition. It has been demonstrated that concentrations of these contaminants are often higher in produce from farms close to urban areas or industrial facilities, e.g. milk (Ball et al., 1993, Ministry of Agriculture Fisheries and Food, 1997). In addition to aerial deposition, transfer through river systems may also be important as sediment in river systems can serve as a sink for PCDD/Fs and PCBs and then provide a long term source of release (Fattore et al., 2002). Studies of PCDD/F and PCB loadings in the sediments of rivers worldwide have confirmed this (Fattore et al., 2002, Zhang et al., 2008). Flooding of land by river water carrying PCDD/F and PCB contaminated sediment has been demonstrated to be an important source of localized contamination (Lake et al., 2005), providing another pathway for transfer to the human food chain. Milk produced on flood-prone land on industrial river catchments has elevated PCDD/Fs and PCBs (Lake et al., 2005). This study represents the first controlled investigation into potential contaminant transfer to beef cattle grazing on flooded pastures. It explores whether overbank flooding of grazing land might influence the concentration of PCDD/Fs and PCBs in animals reared using conventional animal husbandry techniques. Beef products, specifically carcass meat, are important commodities in the diet of the UK and many countries. The aims of the study were:
- 1.
to establish whether flooding has an impact upon PCDD/F and PCB concentrations in meat of beef cattle
- 2.
to provide supporting evidence by analysing matched samples of soil, grass and commercial feed samples from each farm.
Section snippets
Study area
The study focused on the Trent and the Aire/Ouse river systems in central England. The locations of these are presented in Fig. 1 and both flow through substantial urban and industrial areas. The figure also shows that there are many rural areas within these catchments. Previous research has demonstrated elevated PCDD/Fs and PCBs on flood-prone pasture at farms next to the river Trent (Lake et al., 2005). No comparable reports have been published on the Aire/Ouse river system. Maps of beef farm
Results
The distributions of total TEQ (sum of PCDD/F and dioxin-like PCB TEQ) in meat, soil, grass and commercial feed are presented in Fig. 2. The meat data (Fig. 2a) demonstrated large variations in total TEQ concentrations with median levels of 2.94 (ng TEQ/kg fat) and range of 0.31–8.85 (ng TEQ/kg fat). The median value was less than the mean indicating that the distribution had a long right tail with a majority of lower values and a few higher ones. The soil data (Fig. 2b) also presents a skewed
Discussion and conclusion
Most of the evidence in Table 2 suggests that river flooding leads to elevated PCDD/F and PCB levels in meat. PCDD/F and PCB levels were higher in soil from flood prone farms and most farm pairs had higher soil total TEQ on the flood-prone farm. This result was consistent between river systems. Furthermore, on one field soil total TEQ was higher on the flood-prone part of the field in comparison to a location on the field that was not flood-prone. Comparable results for grass were not as strong
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