Environ. Sci. Technol. 1999, 33, 371
Response to Comment on “Identification of Estrogenic Chemicals in STW Effluent. 1. Chemical Fractionation and in Vitro Biological Screening” SIR: The presence of natural and synthetic steroidal estrogens in the aquatic environment was reported previously (1-3). However, our lastest findings have received considerable interest because these compounds were identified as being the main causal compounds responsible for the estrogenic activity of domestic STW effluent (4) and were shown to occur at levels capable of producing biological effects in fish exposed via the water (5). Steroidal estrogens are classified as micropollutants, a term commonly associated with compounds which occur in the environment in the low ng/L range, and which may not have been regarded as being environmentally relevant for this reason. An extensive number of synthetic chemicals, used in a wide-range of products, are now known to mimic the action of 17β-estradiol. Many of these chemicals (called xenoestrogens) enter the aquatic environment by means of discharge from industrial effluents, municipal sewage-treatment works, and agricultural waste and can occur in effluents and rivers from nanogram to mg/L levels. Bearing this in mind, it is probably not surprising that one of the most obvious sources of estrogen, 17β-estradiol and its metabolites, may have been overlooked. Very little is known about the fate, behavior, and persistence of steroidal estrogens after excretion, during the STW process, or following their discharge into rivers and other surface waters. Laboratory experiments suggest that steroidal estrogens are poorly degraded during the STW process (6), and, therefore, the extent to which this happens will depend largely on the length of time that they are exposed to the activated sludge. As the sewage-treatment process can last for less than 24 h in some cases, significant biodegradation of steroids may not occur following aerobic and anaerobic treatment, and it is likely that most removal from the water probably occurs via sorption or other mechanisms independent of biodegradation. Recent research also confirms that certain microorganisms (such as E. coli) present in sewage sludge can effectively transform glucuronated estradiol (which is not estrogenic) into a form capable of stimulating an estrogenic response (VTG production) in fish (personal communication, Grace Panter). Therefore, it is very easy to envisage why unconjugated steroidal estrogens might occur in STW effluent, but many questions need to be answered if this issue is to be better understood. As steroidal estrogens are present in domestic STW effluent, it is concievable that other type of steroidal compounds might also be present. Indeed, our preliminary findings indicate that effluent contains approximately equivalent levels of androgenic activity in vitro (also believed to be steroidal in nature and therefore presumably deconjugated). Thus, effluents and rivers may contain a complex mixture of steroid hormones and their derivatives. It is encouraging that the concentrations of steroidal estrogens measured in our study of domestic STW effluents lie within the boundaries of the theoretical calculations reported by Johnson and co-workers and indeed suggest a † ‡
Brunel University. Burnham Laboratory.
10.1021/es982016j CCC: $18.00 Published on Web 12/10/1998
degree of removal by the STW process. However, it is apparent that these types of calculation are greatly influenced by the actual excretion figures used. For example, if the excretion figures reported by Arcand-Hoy and colleagues (7) are used in the same calculation (where a normal female is reported to excrete between 10 and 100 µg E2/day depending on the phase of the menstrual cycle, and pregnant women release as much as 30 mg E2/day), then it appears that the efficiency of English STWs to remove steroidal estrogens probably exceeds 90% in all cases. Thus, although these types of calculations are interesting, they may be also a little premature. An accurate determination of the removal efficiency of steroids during the STW process will require the determination of actual levels of steroidal estrogens in both the influent and the effluent. Nevertheless, it is clear from these studies that the efficiency of STWs to degrade and remove natural and synthetic steroidal estrogens needs to be improved further, because the proportion which remains in the effluent is capable of producing biological effects. This fact is even more important when we consider that effluent can constitute a significant proportion of river flow, particularly in summer months. Although we have emphasized above the need to be cautious about drawing conclusions from theoretical calculations based on limited data, we will now attempt some extrapolations ourselves! It has been proposed that an average human inhabitant (representative in age and sex of the entire population) excretes 114 µg of total endogenous estrogen per day (a figure obtained from an as yet unpublished study). As the world population is approximately 6 billion people, humans alone would excrete 249 660 kg (550 000 pounds; ca. 275 American tons) of estrogen per year. This figure might be doubled or trebled when the contributions by farm animals are also considered. These figures suggest that endogenous steroidal estrogens, such as 17β-estradiol, should theoretically be added to the list of 15 000 priority chemicals which will be screened as part of the EDSTAC process over the next two years. It would be interesting to see if the results of this screening exercise suggest that steroidal estrogens are a risk to aquatic wildlife, and hence their use should be phased out!
Literature Cited (1) Tabak, H. H.; Bloomhuff, R. N.; Bunch, R. L. Dev. Ind. Microbiol. 1981, 22, 497-519. (2) Shore, L. S.; Gurevitz, M.; Shemesh, M. Bull. Environ. Contam. Toxicol. 1993, 51, 361-366. (3) Stumpf, M.; Ternes, T. A.; Haberer, K.; Baumann, W. Vom Wasser 1996, 87, 251-261. (4) Desbrow, C.; Routledge, E. J.; Brighty, G. C.; Sumpter, J. P.; Waldock, M. Environ. Sci. Technol. 1998, 32, 1549-1558. (5) Routledge, E. J.; Sheahan, D.; Desbrow, C.; Brighty, G. C.; Waldock, M.; Sumpter, J. P. Environ. Sci. Technol. 1998, 32, 1559-1565. (6) Tabak, H. H.; Bunch, R. L. Dev. Ind. Microbiol. 1970, 11, 367376. (7) Arcand-Hoy, L. D.; Nimrod, A. C.; Benson, W. H. Int. J. Toxicol. 1998, 17, 139-158.
Edwin J. Routledge,*,† John P. Sumpter†
Mike
Waldock,‡
and
Department of Biology and Biochemistry Brunel University Uxbridge, Middlesex UB10 0DZ, U.K. Centre for Environment, Fisheries and Aquaculture Science, Burnham Laboratory, Remembrance Avenue Burnham-on-Crouch, Essex, CM0 8HA, U.K. ES982016J
1999 American Chemical Society
VOL. 33, NO. 2, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
371
