Natural Steroid Hormones

Livsetsock wastes can be termed as natural agricultural waste and can act as potential sources of EDCs (Figure 1) to the environment. Compounds such as E2, its metabolites E1 and estriol (E3), and male androgen testosterone and its derivative androstenedione are excreted by animals of all species. These hormones are present in faeces and/or urine and reach the environment through the release of animal wastes to receiving waters, animal waste application onto land, or by direct excretal input while grazing (Sarmah et al. 2006). While all species of farm animals excrete these hormones, different species excrete different types and proportions of estrogens. For example, in cattle (Bos Taurus) > 90% of estrogens are excreted as 17a-estradiol, 17P-estradiol, and estriol as free and conjugated metabolites, while pigs (Sus scrofa) and poultry (Gallus domesticus) excrete estradiol, estriol and estrone, and their respective conjugates (Erb et al. 1977). The amounts of hormones excreted by various animals depend on their reproductive stage and the route of excretion, fecal or urinary (Hanselman et al., 2003). Table 2 summarizes the estimated amount of EDCs excreted by a dairy cow of typical weight of 640 kg at different stages in its reproductive cycle.

Figure 1. Molecular structures of steroid hormones and their degradation products. The numbers represent carbon position.

Dairy cattle and other animals excrete steroid hormones as free and conjugated compounds. Conjugation of steroid hormones to their respective glucuronides (addition of glucose) and/or sulphate form (by addition of sulphate) neutralises their activity and enhances their removal from the bloodstream via the kidneys. To date, very limited data are available on the proportion of steroid hormones excreted by dairy cattle as free and conjugated metabolites, and how this may be affected by their oestrous cycle, pregnancy, and lactation. It is generally accepted that conjugated forms of steroid hormones are rapidly converted to their respective free and active forms on excretion and release into receiving environments. Many microorganisms have the ability to rapidly de-conjugate a wide range of organic compounds, and it is reasonable to assume this occurs for steroid hormones. However, studies investigating these processes are limited due to the significant analytical challenges inherent in the analysis of conjugated steroid hormones.

The concentration of 17P-estradiol in various dairy wastes ranges from below detectable limits (BDL) to hundreds of ^g/kg, and is comparable to levels measured in other animal wastes (Table 2). Typical levels of steroid hormones in waste from dairy cows are reported as 39 ^g/kg of estrone and about 18 ^g/kg of 17P-estradiol. Typical slurry pit concentrations of 1.5 ^g/L were obtained for 17P-estradiol, while the concentration of estrone was 3-fold higher (Raman et al. 2004).

Table 2. Estimated rates of fecal and urinary estrogen excretion from dairy cattle (Source: cited by Hanselman et al. 2003)

Reproductive stage

No of

Excretion rate/

Measured

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