Paper of the week: Effects of prenatal exposure of pthalates

Pthalates are esters of pthalic acid that are commonly added to plastics but also are found in diverse products ranging from cosmetics to pharmaceutical pills. As could be expected, studies that monitor phthalate metabolites in human populations have shown that they are widely present. Over the years, there have been many concerns over their effect on human health notably as hormonal disrupting agents. This has led to the regulation of some phthalates in consumer products in Europe and the United States, which in some cases,have been replaced with others. Recent evidences indicate that endocrine disruption might only be a tip of the iceberg and that pthalates might have other health effects as well.

It is well known that maternal exposure of pollutants make their way to the offspring and in many cases can have deleterious consequences. It appears that this dogma can also be applied to the case of the pthalates. In a study by Engel et al published in Environmental health perspectives,

http://ehp03.niehs.nih.gov/article/fetchArticle.action;jsessionid=E899A81379071E8E095EF53E962F597F?articleURI=info%3Adoi%2F10.1289%2Fehp.0901470

the authors questioned whether there was any association between prenatal phthalate exposure to the behavior of offspring. The study occurred in a multiethnic prenatal population enrolled in the Mount Sinai Children’s Environmental Health Study in New York City between 1998 and 2002. Urine samples of mothers during the third-trimester of pregnancy was collected and analyzed for phthalate metabolites. Subsequently, cognitive and behavioral development of the children was assessed between the ages of 4 and 9. Interestingly, the scientists found that increased concentrations of low-molecular-weight (LMW) phthalate metabolites in the mothers were associated with poorer scores on aggression, conduct problems, attention problems, and depression in the children. These results led them to conclude that behavioral domains adversely associated with prenatal exposure to LMW phthalates in this study are commonly affected in children clinically diagnosed with conduct or attention deficit hyperactivity disorders.

This study and several of its predecessors, extend the known adverse effects of pthalates, which calls for increased caution. What is urgently needed are more hard core studies elucidating the toxicology of pthalates and their metabolites, that will help us understand the consequences of exposure. However, these studies will take time; the evidence at hand should motivate nations to re-evaluate their policies on pthalates and enforce strict regulations.

Engel SM, Miodovnik A, Canfield RL, Zhu C, Silva MJ, Calafat AM, & Wolff MS (2010). Prenatal phthalate exposure is associated with childhood behavior and executive functioning. Environmental health perspectives, 118 (4), 565-71 PMID: 20106747

Paper of the Week: Humans and Biodiversity

A new study interestingly implies that human activities may not always be bad for biodiversity. Long before the colonizers arrived in South America, indigenous farmers, belonging to the Arauquinoid cultures, had already interfered with the Amazonian biodiversity. Their novel agricultural engineering methods had changed the savannah ecosystem, resulting in increased biodiversity. Thus states the solid paper, on 'Pre-Columbian agricultural landscapes, ecosystem engineers, and self-organized patchiness in Amazonia', published in Proceedings of the National Academy of Sciences (online before print, April 12th 2010), by Doyle McKey (Université de Montpellier II, France), Stéphen Rostain, José Iriarte, Bruno Glaser, Jago Jonathan Birk, Irene Holst, and Delphine Renard. The savannahs of coastal Guyana tend to flood during the rains and are dry during the summer. However, strange complexes of mounds are seen in the terrain of these plains, running for 360 miles from Berbice River to Cayenne. Due to their perfect symmetry, the mounds were deduced to be man-made. The mounds drained well during the rains and floods (their drainage capacity was nine times as high as the seasonally flooded savannah). The authors deduce that these are large raised beds/fields, made out of the surrounding topsoil, for cultivating crops (a theory further substantiated by soil samples containing microfossils of maize, cassava, and squash), constructed by the pre-Columbian farmers, around 1000-700 years ago. The interesting point is that this farming was practiced in wastelands considered to be unsuitable for agriculture- a feat achieved due to their effective agricultural engineering. When these fields were abandoned, the mounds were colonised by flora and fauna, thus creating a new ecosystem. These 'ecosystem engineers' (viz., ants such as Acromyrmex octospinosus and Ectatomma brunneum, termites such as Nasutitermitinae, and earthworms) built their nests on the raised beds so that the colonies wouldn't be flooded. Their burrowing aerated it further, helping in accumulating sufficient rainfall. Moreover, the mounds were fertilised as a result of them congregating organic matter into their nests and accumulating minerals such as nitrogen, potassium, and calcium. As a result, the perennial plants on the mounds flourished and their strong roots prevented the erosion of the mound. All of these alterations initiated by humans have resulted in a higher biodiversity than seen in the normal savannahs. This study would give additional impetus to the debate over whether most of the Amazon rainforest and savannahs (commonly considered to be pristine) are sites of significant human occupation, especially during the pre-Columbian times. The authors suggest that this agricultural system could be a model for modern farming, especially considering the beneficial ecological changes. Although this is a perfect example of a terrain modified by humans and maintained by Nature, it must be noted the increase in biodiversity was a result of 400-800 years of no/minimal human intervention. Secondly, the ‘punja’ technique of rice/paddy cultivation has a very similar methodology and is followed in parts of Kerala. link: http://www.pnas.org/content/early/2010/04/07/0908925107.abstract?sid=93317154-3ce6-43c8-9a1e-456e24272c2b

McKey D, Rostain S, Iriarte J, Glaser B, Birk JJ, Holst I, & Renard D (2010). Pre-Columbian agricultural landscapes, ecosystem engineers, and self-organized patchiness in Amazonia. Proceedings of the National Academy of Sciences of the United States of America, 107 (17), 7823-8 PMID: 20385814

Synergy

When scientists study a situation there is a tendency to regard each factor in isolation, on the very reasonable grounds that it is both easier and clearer. The real world however, rarely works like that and factors are often synergistic, that is the effect of their combination is greater than either alone. For example a combination of two anti-cancer drugs may be required to knock out a tumour´s resistance and to kill it, neither drug is effective alone. A recent paper from the Smithsonian Tropical Research Institute draws attention to how this might apply to tropical forests.
http://www3.interscience.wiley.com/journal/123190996/abstract?CRETRY=1&SRETRY=0

Consider logging, hunting and fire. Logging of tropical forests of course destroys habitat, but in those rare examples where it is controlled the loss of species is less than you might think, they often still persist in any remaining fragments. Hunting in pristine forest tends to hampered by difficulty of access, and large scale fire is relatively rare as the canopy keeps lower levels damp and hard to burn. However logging needs roads and this opens up previously inaccessible areas to hunters, as well the as the effect of loggers themselves. It is estimated that a single logging camp in Indonesia consumed 33,000 kg of bushmeat per year. Ease of access and increased demand together can devastate animal populations, particularly of large animals.
Logging also opens the forest canopy, drying out the undergrowth beneath, and greatly increasing the chance of fire. Most tropical forest plants lack the fire defences such thick bark or fireproof seeds of pampus species, and so are wiped out by fire.

Another example is the way that native species can be exposed to foreign pathogens imported by humans from elsewhere, a form of "pathogen pollution". Native species of have no, or very little, natural immunity to these diseases. As with the great human plagues of the middle ages, this can devastate whole populations. Animals in small habitats fragmented by logging or agriculture can be wiped out. To make matters worse, many diseases are exacerbated by "environmental stressors" such as pesticides, UV, and pollutants damaging the immune system

The world is a very very complicated place, events combine in unexpected ways, and the Law of Unexpected Consequences is as draconian as it ever was. We need to be aware of this in our thinking.