MiSSE addresses both the exposure to cats and to small children by the analysis of dust samples, and establishing the exposure pathway by analysis of cat serum. Focus of the project is to identify thyroid hormone disrupting compounds in our indoor environment, a health effect highly relevant for both humans and cats which has gained more attention internationally lately as a societal challenge of concern.
In 2007, Prof. Birnbaum and her colleagues published an article suggesting that cats’ increasing incidence of Feline hyperthyroidism (FH) could be due to chemical exposure indoor (Dye et al 2007). This suggestion was in addition to earlier veterinarian epidemiologic studies that had reported associations of FH to indoor living habits (e.g. litterbox), consumption of canned cat food, in particular fish flavors, and use of flea powders and sprays (Norrgran Engdahl Thesis 2015).
Prof. Birnbaums group reported the levels of brominated flame retardants, i.e. the polybrominated diphenyl ether (PBDEs) in the blood serum of healthy cats and in cats diagnosed with FH. The hypothesis was that these compounds caused FH, as it was observed that the introduction of PBDEs in household products coincide to the increasing trend of FH in cats in the US. The results revealed that the PBDE levels were between 20 and 100 times higher than in the average US population (adults). Although they could not find a correlation between the cat’s health status and the PBDE levels (due to small sample set and high variability), they did conclude that the cats are exposed to high levels of compounds with hormone disrupting potency.
This study was also the first to suggest that cats could be used as a sentinels to better assess the chemical exposure small kids have in our homes. Both cats and kids ingest more dust than adults, due to their grooming and hand-to-mouth behavior, respectively. On an average, kids ingest around 40 mg dust per day (up to 200 mg), which is twice as much as an adult. There are no measurements performed on cats to establish their daily intake of dust, but it is reasonable to believe that their intake of dust is even higher than 40 mg/day.
To follow-up on that, a larger sample set of cat serum from the University Animal Hospital in Uppsala, Sweden was collected in 2010, and analyzed for a range of brominated and chlorinated organic contaminants. Dr. Norrgran and coworkers could demonstrate with that dataset that FH cats indeed had higher serum levels of certain PBDEs, as well as a polychlorinated biphenyl (PCB). That study was the starting point of the MiSSE project.
In short, the research objectives of the MiSSE project can be summarized by two questions:
Is dust an exposure pathway to hormone disruptors, mainly focusing on thyroid hormone disrupting compounds (THDCs)
Is the exposure of the mixture of THDCs associated to dust of concern?
In 2011, partners from four universities, i.e. Stockholm university, Umeå University, VU university of Amsterdam, and the Swedish university of agricultural science (SLU) in Uppsala got together and formulated the outline of the projects. It was early decided that it should be focusing on the thyroid hormone system, one of the endocrine systems involved in several crucial functions of the organism.
Thyroid hormones play an important role in the maintenance of a normal physiological state and are essential for metabolism and growth. Especially exposure during early life stages is critical, as it can effect health outcomes throughout the whole life, such as effecting puberty, reproduction, diabetes and menopause onset. Chemicals that interfere with the normal function of thyroid hormones could have effects both on individuals, as well as on whole populations.
In our daily life we are continuously exposed to mixtures of chemicals from our surrounding environment, some voluntary (e.g. pharmaceuticals and personal care products) and some without our awareness (e.g. plasticizers, surfactants, flame retardants, antibacterial agents, antioxidants and many others), leaking out from household products, indoor materials and goods. Many of these compounds have been shown to be reflected in household dust, and many of these are also endocrine disrupting compounds.
The MiSSE (Mixture aSSessments of EDCs) project was granted and started in 2012. The strength of the project is that we decided to use so-called paired sampling. That is, when we visited the participating families we took blood serum samples from cats and dust samples from the household at the same time. By using paired sampling we had a statistically more powerful sample set to evaluate dust as the exposure route to these compounds. Thus, we did not investigate healthy and hyperthyroid cats this time, but all cats were examined at the sampling occasion and was judged as healthy. This was also later confirmed by analysis of the blood status.
In MiSSE we wanted to establish dust as the exposure pathways to cats, and consequently estimate the indoor exposure for small children. We cannot assume that the uptake and distribution is identical between the two biological systems, the metabolic capacity is very different between carnivores and omnivores, but we do believe that cats can be a model for the initial exposure.
Secondly, we wanted to examine whether the exposure of the mixture of chemicals that was found in dust, as well as in the cat serum, could pose a risk for the health of the cat. Again, the toxic profile of these chemicals can differ between cats and children. Optimally the estimated effects in the project should be further investigated for extrapolation towards human exposure and health effects. That was not within the scope of MiSSE, but could well be the next step of the project.
MiSSE project will end in December 2018 and we are currently finalizing the separate studies. Everything is not yet fully evaluated and publications will come also after 2018. Whenever new data is published, we aim to update the section accordingly.