Figure 1. Log-transformed E2 production values for humans in comparison to that for 63 non-domestic non-human mammalian species assuming non human species exhibit a per capita production equivalent to that of pigs.

orders of magnitude less than that of E2 (e.g., 1x10^-4). Most of the estimated excretory rates I found applied only to domestic animals. Research is badly needed to determine the rates at which non-domestic non-human species produce estrogen to better compare humans with such species.

To make our inter-specific comparisons conservative, we assumed that the rate at which individual pigs produce estrogen is the rate at which individuals of wild species produce this hormone. The per capita production of estrogen by pigs was found to be approximately 10% of that for cattle. Sheep produce even less (approximately 3% and closer to the rates humans produce estrogen physiologically). The per capita value for pigs was then used to estimate total estrogen production for 63 other, non-domestic species - all of approximately human body size (population data from Fowler and Perez, 1999). This resulted in the graph seen in Figure 1 which compares human physiologically produced E2 (per capita rates from Johnson et al. 2006 with an assumed human population of 6.6 billion) with that for the other species.

Figure 2. Estrogen production by domestic cattle compared to that of 63 wild species which are assumed to produce estrogen at the same per capita rate as cattle.

In agricultural practice, are cattle (or other species) producing estrogen at normal rates compared to other species?
Figure 2 shows a comparison between estrogen production by cattle and that of the same 63 wild species of Figure 1 (with estimates of global cattle population from another component of my summer's work - 1.37 billion). In this graph we assumed that the wild species produce estrogen at the same per capita rate as cattle. The striking abnormality shown in this graph is less extreme than if the comparison involved the pattern of Figure 1.

Industrial chemicals were not included in the calculations for human production of estrogenic compounds for comparison in Figure 1. It is nearly impossible to determine how much of any industrial compound actually gets into the environment. Since many of the estrogenic chemicals are contained in plastics, environmental contamination involves seepage from the products. As an area of concern, a great deal more research is needed.

Chemicals which are known to have estrogenic properties are found in insecticides (DDT, endosulfan, and toxaphene), plastics (Bisphenol A and a variety of phthalates), surfactants (nonylphenol and octylphenol), and flame retardants (a variety of brominated compounds). For the few compounds for which I could find estimates of production, the combined E2 equivalent is at least as large as the amount humans produce physiologically, and probably much more. Many of the compounds are known as highly toxic environmental pollutants with significant health risks, and, therefore, are being produced in much smaller quantities than earlier. DDT production alone (E2 equivalent) in 1990 was approximately equivalent to current physiological estrogen production by humans.

Even without taking industrial chemicals into account, humans still produce more (over 54,000 kilograms/year) physiologically than any other large mammal (Fig. 1). My research contributes to understanding the magnitude of human impact on ecosystems. We humans, as in so many other ways, do not fit in with other species in our production of estrogenic compounds. While the exact amount of industrial estrogenic chemicals we produce is not known, we know that there are effects. The effects on aquatic species are most well understood, because so much of our waste ends up in streams and lakes where a number of studies have shown effects (Arukwe and Goksøyr, 1998).

I enjoyed my time as an intern at the AFSC. I met some fantastic people, both other interns and NOAA scientists. I look forward to seeing my work published in Dr. Fowler’s book about systemic management.

References:

-Arukwe, A., and A. Goks?yr. 1998. Xenobiotics, xenoestrogens and reproduction disturbances in fish. Sarsia 83(3):225-241.

-Cargou?t, M., D. Perdiz, A. Mouatassim-Souali, S. Tamisier-Karolak, and Y. Levi. 2004. Assessment of river contamination by estrogenic compounds in Paris area (France). Science of the Total Environment 324(1-3):55-66.

-FAOSTAT. ProdSTAT: Live animals. 2006. http://faostat.fao.org/site/568/default.aspx

-Fowler, C. W. and M. A. Perez. 1999. Constructing Species Frequency Distributions - a step toward systemic management. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-109, 59 p. (View document (.pdf, 1.33MB)

-Ingerslev, F., E. Vaclavik, and B. Halling-Sorensen. 2003. Pharmaceuticals and personal care products: A source of endocrine disruption in the environment? Pure and Applied Chemistry 75(11-12):1881-1893.

-Johnson, A. C., R. J. Williams, and P. Matthiessen. 2006. The potential steroid hormone contribution of farm animals to freshwaters, the United Kingdom as a case study. Science of the Total Environment 326(1-3):166-178.

-Lange, I. G., A. Daxenberger, B. Schiffer, H. Witters, D. Ibaretta, and H. H. D. Meyer. 2002. Sex hormones originating from different livestock production systems fate and potential disruption activity in the environment. Analytica Chimia Acta 473(1-2):27-37.