## 2 Endocrine Disrupting Compounds (EDCs) in the Environment and Associated Risks  
Endocrine disrupting compounds (EDCs) are natural or synthetic substances that, when introduced into the environment, affect the endocrine and homeostatic system of non-target organisms by disabling their communication and response to environmental stimuli. These include estrogens- natural and synthetic female and male hormones that play an important role in both the reproductive and the non-reproductive systems [3; 6; 9]. Estone, estriol and 17\(\beta\)-estradiol are natural estrogens. The latter is considered to be the strongest among the endocrine factors in the environment [10]. Synthetic estrogens have been divided into steroidal, such as 17\(\alpha\)-ethynylestradioliol and 3-methyl ether of ethynylestradioliol, used as ingredients of birth control pills, and nonsteroidal estrogens such as diethylstilbestrol used to prevent miscarriages [3; 7; 11]. Human use of the latter was banned in 1972 due to its negative effects, however, it is still used in China as a growth promotor for terrestrial livestock or fish [11]. The presence of estrogens has been reported in many aquatic environments (Table 1). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**EDCs** & **Concentration** & **Occurrence** & **Sampling Period** & **References** \\ \hline \multirow{2}{*}{Estone} & \multirow{2}{*}{10.4 ng/L} & Leca River (Portugal) & Spring to autumn & [4] \\  & & & Leca River (Portugal) & Spring to autumn & [4] \\  & & & Leca River (Portugal) & Spring to autumn & [4] \\  & & & Leca River (Portugal) & Spring to autumn & [4] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Wuluo River (Taiwan) & December to May & [12] \\  & & & Surface water of & & \\  & & Taihu Lake, China & May & [13] \\  & & & Sediments of Taihu & & \\  & & & Lake, China & \\  & & & Lake Balaton, & \\  & & & Hungary & \\  & & & River Zala, & \\  & & & Hungary & \\  & & & Yangtze estuary, & \\  & & & China & \\  & & & Themi River, & \\  & & & Tanzania & \\  & & & Kalansanan River, & \\  & & & Malaysia & \\  & & & Fenholloway River, & \\  & & & USA & \\  & & & & \\  & & & & \\  & & & \\  
One of the main sources of estrogens in a highly urbanized environment is urine and faeces getting into wastewater. It has been shown that annually 33 and 49 tonnes of estrogen excreted from farms in the European Union and the United States, respectively, are released into the environment [12; 20]. In human and animal organisms, estrogens are usually hydroxylated or conjugated with glucuronide or sulfate hence these forms most often get into wastewater. It is estimated that about 90% of urine estrogens are in the form of conjugates. Most estrogen conjugates are more polar than parent molecules, so they can be more mobile in the environment. Despite the fact that conjugates have low estrogenic potential, they can be chemically or enzymatically hydrolysed to active forms in the environment. For example, the _Escherichia coli_ strain KCTC 2571 has \(\beta\)-glucuronidase, which cleaves glucuronide moieties, releasing free estrogen [20; 21]. As a result of the operation of sewage treatment plants, 19-94% of estrogens are biodegraded and biodtransformed. Typically, concentrations in the range of 1-3 ng/L are observed in the effluents from treatment plants [3]. Although these compounds occur in the environment in concentrations of ng/L, it is known that they can have a strong negative impact in amounts below 1 ng/L because they have a high affinity for nuclear estrogen receptors. This biological activity can lead to low levels of estrogen in the environment causing endocrine disorders in the wildlife population.