Wednesday, 30 January 2013

Pussy Cat, Pussy cat, what have you killed?

In the early eighties, our parents rescued two abandoned stray kittens from the road, which started a long line of cat dynasty in our house and the neighbourhood. Our house gained the reputation of being a sanctuary for abandoned cats, that we had people stealthily abandoning their cats outside our house gates. At one point, we had about 12 cats in the house. We loved these animals dearly; but despite being fed adequately, we were horrified to note that they killed squirrels, birds, bats, bandicoots, rats and mice. We lamented their notorious habit of murdering birds and squirrels, particularly as we fed them too, and could never comprehend how our adorable pets could turn into merciless masochistic killers, particularly as they never ate their kill. The carcass was presented for us to see almost very time.  I remember one time when my mother was inconsolable, when a cat killed one of ‘her’ doves that she had grown so attached to. Our repeated efforts to teach the cats 'good behaviour' was not fruitful.  

The  results presented in recent paper in Nature Communications by Loss and his colleagues on the 'The impact of free-ranging domestic cats on wildlife of the United States' was not a surprise in one respect ,as we all know that cats kill birds and smaller mammals. However, what was surprising was the magnitude of the effects. Domestic cats have been introduced globally by man and are linked to the extinction of several animals on islands, whilst their effect on other places had not been scientifically estimated. In their study, the authors estimate that in the US, domestic cats alone kill 1.4-3.7 billion birds and 6.9-20.7 billion mammals every year, and that cats that are not owned (feral cats) as opposed to owned pets, cause the majority of the killing. What is different about the study when compared to previous ones, is the actual quantification the authors conducted, which suggest that cats cause significant and substantial wildlife mortality than previously thought. Interestingly, these cute and cuddly creatures which are the most popular pets in the world are the primary and greatest source of anthropogenic (caused by humans- in this case indirectly) mortality for US birds and mammals. This makes me wonder, whether their new found notoriety would affect their popularity as pets. For some reason, I doubt it.

2. Loss, S., Will, T., & Marra, P. (2013). The impact of free-ranging domestic cats on wildlife of the United States Nature Communications, 4 DOI: 10.1038/ncomms2380

Sunday, 20 January 2013

Snow in Britain

Britain has had an onslaught of snow since last Friday. Here are some snaps from the Midlands.

Saturday, 19 January 2013

A dangerous cocktail brews in our towns and cities- How tobacco smoke and vehicular emissions together contribute to wheezing in young children

Vehicular emissions and tobacco smoke are harming the lungs of young children  in our cities

When it comes to the evidence against tobacco and vehicular emissions on harming human respiratory health, it does not rain but it pours. And it keeps on coming. We have extensive evidence to show that vehicular emissions as well as tobacco smoke exposure are bad for health and it seems to start right from the fetal stage.  A new study presented in the journal Environmental Health shows that exposure to traffic-related air pollutants is associated with increased risks of wheezing in children who are exposed to tobacco smoke in fetal  life and infancy indicating an axis of villains who co-operate to exert their  harmful effects.

The study was a large prospective cohort study involving 4,634 children in Rotterdam, the second largest city in the Netherlands.  One of the largest ports in the world, it is also one of the most polluted places in the Netherlands and an apt location for pollution studies. A prospective cohort study is one that monitors a group of similar individuals –cohorts- who differ in certain factors under study over a time period in order to understand how these factors affect rates of a certain outcome- in this study, how effects of vehicular emissions, tobacco smoke exposure (in any stage starting from fetal life to the age of 3 years) affect wheezing in children.

Many cities, like this one, has air pollution monitors that helps scientist understand how air pollutants affect human health .
 Particulate matter (PM) of the size of 10 microns or less can penetrate the deepest part of the lungs such as the bronchioles or alveoli. Domestic coal combustion was once the major source of particulate emissions, but recently other sources such as road transport are important sources with diesel vehicles notably emitting increased levels. Road vehicle exhausts, off road equipment, and power plants  are  important sources of NO2.  In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system. In this study, the exposure of children to particulate matter (PM10) and nitrogen dioxide (NO2) were assessed by analysing emission data at the home address. Parents were asked to fill questionnaires that indicated whether their children had wheezing until the age of 3 years.  Parents were also asked to provide information on whether the fetus or the baby had been exposed to tobacco smoke either through the mother or the partner smoking tobacco.

Results from the study indicated that average annual PM10 or NO2 exposure levels per year were not associated with wheezing in the same year.  Even though there were trends showing a link with PM10 or NO2 exposure levels and wheezing during the first 3 years of life, the results were not statistically significant. The researchers did not observe associations of traffic-related air pollutants with wheezing among children who were exposed to smoke during fetal life only or during infancy only. But in children who were exposed to tobacco smoke in both fetal and infant stage, PM10 or NO2 exposure levels was associated with wheezing during the first 3 years of life. The scientists did not observe associations of traffic-related air pollutants with wheezing among children who were not exposed to tobacco smoke.

There are limitations in the study, one of  which the researchers have noted viz. the possibility of ‘misclassification of air pollution assessment’ owing to the analysis only  involving  exposure levels at home addresses and not at the day care centers or other places where the child may spend days and nights. One factor that could have further added value to the study is blatantly missing- work addresses of mothers and PM 10, NO2 levels  - and whether when analysed together with air pollution exposure at home had any links to wheezing in children.

Nevertheless the study extends our understanding on how air pollution and tobacco smoke exposure contribute to the health of younger children. The  results suggest that long term exposure to traffic-related air pollutants is associated with increased risks of wheezing in children exposed to tobacco smoke in fetal life and infancy. Tobacco smoke exposure in early life might lead to increased vulnerability of the lungs to air pollution. The evidence appears to show that exposure of fetus and  infant lung to tobacco smoke primes it for damage by air pollutants leading to wheezing suggesting that the dangerous cocktail is made more potent by the ingredients together.


Sonnenschein-van der Voort, A., de Kluizenaar, Y., Jaddoe, V., Gabriele, C., Raat, H., Moll, H., Hofman, A., Pierik, F., Miedema, H., de Jongste, J., & Duijts, L. (2012). Air pollution, fetal and infant tobacco smoke exposure, and wheezing in preschool children: a population-based prospective birth cohort Environmental Health, 11 (1) DOI: 10.1186/1476-069X-11-91

Wednesday, 9 January 2013

Exposure to air pollutants during pregnancy linked to autism in children

Vehicular air pollution could cause autism - Photo by Sarah Stephen

A recent study by Californian researchers indicates increased odds for developing autism in children whose mothers were exposed to ozone and particulate matter 2.5 (PM2.5). Ozone and PM2.5 are associated with vehicular pollution and this study emphasizes the dangers posed by traffic pollutants to health in utero.

The researchers used Los Angeles as a sample population. Mothers of over 7600 children between ages of 3-5, diagnosed with autism during 1998-2009, were identified and their addresses at the time of pregnancy established. For each case, 10 controls were used in the analysis, and the addresses of the mothers were linked with air monitoring stations in the vicinity. The researchers then used using data from air monitoring stations and a land use regression (LUR) model to estimate exposures and came to the conclusion that ambient air pollution is linked to autism. Though LA is much cleaner than it used to be, it frequently has the highest levels of ozone within the country. According to the authors, theirs is the first study to show a link between autism and ozone.

With the increase in the prevalence of autism in the recent years, such an association is of relevance, yet calls for further detailed and stringent studies. Exposure to air pollutants in pregnant mothers has been linked to several diseases in children. In fact, a previous study  linked ambient concentration of solvents and heavy metals near maternal residences to autism in children. The findings of the recent study cannot be taken lightly. However, the problem with many population based studies is that an association doesn't always signify causality, an argument touted by skeptics, and often the hardest to prove otherwise.

Becerra, T., Wilhelm, M., Olsen, J., Cockburn, M., & Ritz, B. (2012). Ambient Air Pollution and Autism in Los Angeles County, California Environmental Health Perspectives DOI: 10.1289/ehp.1205827

Windham, G., Zhang, L., Gunier, R., Croen, L., & Grether, J. (2006). Autism Spectrum Disorders in Relation to Distribution of Hazardous Air Pollutants in the San Francisco Bay Area Environmental Health Perspectives, 114 (9), 1438-1444 DOI: 10.1289/ehp.9120


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