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In the last few decades contraceptives have become well established in Western societies. Especially women benefit from birth control since the ability to plan pregnancies has high implications on a woman’s way of life. In that way it is no wonder that many contraceptive methods are focused on females by taking effect somewhere between preventing ovulation in the first place or preventing nidation after conception.

According to a recent study hormonal contraceptives are among the most popular contraceptive methods in the USA with the contraceptive pill being the most important contraceptive method (Jones et al., 2012). As it seems, progestin contraceptives are en vogue at the moment because there is a growing demand of such drugs. The important active components of combination oral contraceptive pills are estrogens and progestins whereby estrogens primarily regulate menstruation and prevent ovulation to some degree (Erkkola and Landgren, 2005). Progestins (which are synthetic analogs of progestogens like progesterone) are the most important components of the pill because they prevent nidation by (among other effects) altering the viscosity and other properties of the endometrium (Erkkola and Landgren, 2005). Drospirenone, Levonorgestrel, Norethindrone, Medroxyprogesterone and Megestrol are progestins that are frequently used for medical purposes (Vulliet et al., 2008). A daily dose of oral combination pills contains between 0.08 mg to 0.5 mg of progestin (Erkkola and Landgren, 2005).

After the progestin has made its way through the female body it is excreted and is piped (together with the sewage water) to a sewage treatment plant (STP). Unfortunately, due to their chemical properties (like hydrophobicity) and overloading the capacity of STPs progestins remain in the treated effluent of the STPs i.e. in the purified water that enters the water cycle again (Kolodziej et al., 2003). The progestin concentrations in the water of receiving rivers can vary immensely between different rivers of course. For example, Kuster et al. (2008) found a maximum of 1.39 ng/L progesterone in a river near Barcelona, Spain. Kolodziej et al. (2003) have measured up to 14.9 ng/L Medroxyprogesterone in STP effluent with median values at 0.3 ng/L at an undisclosed location in the USA. In a river near Budapest, Hungary, Tölgyesi et al. (2010) found up to 0.37 ng/L progesterone. Vulliet et al. (2008) have tested samples from rivers in the area of Rhône-Alpes, France, and measured up to 2.8 ng/L Norethindrone, a maximum of 7.0 ng/L Levonorgestrel and up to 3.5 ng/L progesterone in surface waters. Kolpin et al. (2002) surveyed surface waters at 139 locations across 30 states in the USA and measured a maximum progesterone concentration of 199 ng/L. Progestins seem to be stable for up to one week once they are discharged to surface waters (Kolodziej et al., 2003).
We do not have any data for Asia, Africa, South America or Australia but we can conclude that progestin at least seems to be present in surface waters all across Europe and North America.

According to the European Agency for the Evaluation of Medicinal Products (1999) all cited progestin concentrations are way below human toxicity and pharmacologically relevant levels (the oral no observable effect level of exogenous progesterone is 160 mg/kg bw/day, the advised maximum intake should not exceed 150 µg/day) and should never pose any danger of death for humans due to low oral bioavailability (less than 10%).

Not only humans and other mammals rely on progestogens for the regulation of reproductive processes though. Fish also use progestins like the pre-ovulatory steroidal pheromone 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20ßP) as pheromones (Sorensen et al., 1990). In their natural environment, female fish secrete 17,20ßP in order to arouse males and evoke mating behavior (DeFraipont and Sorensen, 1993). Mating behavior is “characterized by increased locomotor activity, increased social interaction and decreased feeding” (DeFraipont and Sorensen, 1993). Males that are aroused by 17,20ßP also have increased sperm motility and number thus higher spawining success – this is very important for externally fertilizing species like goldfish (Carassius auratus) because of high sperm competition (DeFraipont and Sorensen, 1993). Since substances like 17,20ßP are important factors for the synchronization of reproduction between females and males (Liley, 1982), male goldfish (C. auratus) have very sensitive progestin-receptors with detection thresholds as low as 0.03 ng/L in order to perceive soon egg-laying by females (Sorensen et al., 1987, Sorensen et al., 1990). In their study on C. auratus Sorensen et al. (1990) found “a strong correlation between structural similarity to 17,20ßP and olfactory potency.” This means that compounds that are structurally similar to 17,20ßP – like Medroxyprogesterone for example– might be able to evoke pheromone-like reactions in fish (Kolodziej et al., 2003).

Due to this possible interaction between progestin receptors and progestins from contraceptive pills and the very low detection thresholds (down to 0.03 ng/L) one cannot rule out the possibility of the initiation of mating behavior by contaminant progestins at environmentally relevant concentrations (see above). Male mating behavior can be regarded as energetically costly behavior because mating behavior distracts males from feeding and exposes them to an increased risk of predation due to higher locomotion (DeFraipont and Sorensen, 1993). Thus, the untimely or even constant initiation of mating behavior by contaminants can be fatal for males.

While exogenous progestins regulate mating behavior and reproductive processes endogenous progestins do regulate important steps like the first meiotic division in oogenesis (Miura et al., 2007) and spermatogenesis (Miura et al., 2006). Thereby, the activation of gametes by progestins is an essential prerequisite for the laying of eggs and fertilization. However, exaggerated exogenous progestin concentrations can have very adverse effects (Runnalls et al., 2013, DeQuattro et al., 2012, Zeilinger et al., 2009):

Fig. 1: Effect of various progestins on female egg production, c(progestin) = 100 ng/L.
Stars denote p < 0.001.
Source: Runnalls et al. (2013)

When Runnalls et al. (2013) exposed several fathead minnows (Pimephales promelas) to progestin-contaminated water especially the progestins Levonorgestrel and Gestodene hat highly significant effects on the clutch size of females (see Fig. 1). Females that were exposed to rather high concentrations of Desogestrel (10 µg/L) completely stopped laying eggs – in contrast, even concentrations as low as 1 ng/L of Gestodene had a significant effect on clutch size (see Fig. 2; Runnalls et al., 2013). Furthermore, females started to develop male secondary sexual characteristics when exposed to 1 ng/L Gestodene (Runnalls et al., 2013). In another study on P. promelas Levonorgestrel heavily affected clutch size at concentrations below 1 ng/L and concentrations around 6.5 ng/L caused 51 % of follicles to become atretic (Zeilinger et al., 2009). Even embryonic development of fish is affected by progestins. In their study Zucchi et al. (2012) were able to show that especially brain development was affected by contaminant progestins in a negative way. In conclusion, even concentrations of contaminant progestin below environmentally relevant levels (see above) can affect sexual differentiation, clutch size, and may even disturb embryonic development of fish. Not only fish are harmed by progestins though. Contaminant progestins can also affect the sexual development of frogs (e.g. Xenopus tropicalis and X. laevis) and cause sterility (Kvarnryd et al., 2011, Lorenz et al., 2011).

Fig. 2: Effect of Desogestrel and Gestodene on female egg production depending on c(progestin) in the medium. Stars denote p = 0.02 for 1 ng/L Gestodene and p < 0.001 for the highest concentrations of both progestins.
Source: Runnalls et al. (2013)

Surface waters usually contain multiple progestins – therefore unexpected synergetic effects cannot be ruled out. Another problem is the accumulation of progestins in blood plasma of fish: Fick et al. (2010) found that the blood plasma of fish living near a STP had progestin concentrations near 12 ng/L while the surrounding water only contained 1 ng/L Levonorgestrel. Thus environmentally relevant concentrations of progestins (see above) might already have dramatic effects on reproductive success and population structures of fish. In that way progestins at presently occurring concentrations in surface waters might seriously damage aquatic ecosystems and disturb natural equilibriums – there might also be various additional effects along the food chain that have not been studied yet.




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