Drugs in Water: A San Francisco Bay Case Study

by Morgan Levy, UC Berkeley, Energy & Resources Group This is one part of a joint Art & Research entry. See the corresponding art piece here.


Hormones, antidepressants, antibiotics, and chemicals from personal care products have been founds in waterways nationwide (1). Most wastewater treatment plants are not equipped to filter pharmaceuticals and personal care products (PPCPs) from treated wastewater and existing treatment processes do so with varying levels of success (2). Thus contaminants not removed during treatment can enter water systems such as freshwater streams and rivers, canals, lakes and reservoirs, groundwater aquifers, estuaries, and oceans (2, 3). Active pharmaceutical compounds are robust and persist in the environment. Pharmaceuticals are specifically made to withstand digestion processes in human (and animal) bodies, and some drug compounds will leave sewage plants at concentrations that are just as strong as when the water entered the sewer system (4, 5). Two studies from the South San Francisco Bay ("South Bay") in northern California demonstrate a geographically specific, yet nationally representative example of how PPCP contaminants enter and persist in our linked natural and human environment.

Where Pharmaceuticals in Water Come From:
  • People: The U.S. represents the largest single national market for pharmaceuticals. Forty-four percent of all Americans take at least one prescription drug, and almost a fifth take three or more (6). Human urinary excretion of intact pharmaceutical compounds can range from the three percent of original intake for a drug like the antiepileptic carbamazepine, to the 90 percent excretion for the beta-blocker atenolol (7). Additionally, medical facilities such as hospitals, nursing homes and dental offices, and institutional facilities like schools, public housing, and correctional facilities release concentrated sources of PPCP compounds into water systems (2).
  • Agriculture: Animals, and especially factory farming operations, introduce PPCPs into water systems. In agriculture, antibiotics are used to treat infections and to promote growth as feed additives (2). Forty percent of U.S.-produced antibiotics are fed to livestock as growth enhancers; livestock manure and un-absorbed antibiotic compounds (often concentrated in massive waste lagoons) eventually wash into surface water or percolate into groundwater (8, 9, 10, 11).
  • Industry: Pharmaceutical manufacturing facilities contaminate water by dumping excess drug compounds. Water from two New York streams that receive discharge from drug manufacturing facilities were found to have concentrations of pharmaceuticals 10 to 1000 times higher than non-receiving water (12).

While many different classes of pharmaceuticals are detectable in water, they are often found at concentrations so low that quantifying their concentrations accurately in samples can be difficult (8, 13). However, the impacts of what even trace amounts of pharmaceuticals can have on both aquatic ecosystems and humans are only beginning to be explored and are little understood (2). Pharmaceuticals have nevertheless been labeled "legacy pollutants of tomorrow" due to their persistence in environments and their ability to build up within the tissues of organisms (14). PPCPs can, like mercury (a more well-understood persistent contaminant), bio-accumulate and move up food chains (4).

  • Environmental Concerns: Pharmaceutical contaminants can cause ecological impacts. USGS scientists found that antidepressants discharged to streams by wastewater treatment plants are taken up into the bodies of fish living downstream of sewage plants (15, 16). Researchers in the UK found that shrimp exposed to the antidepressant fluoxetine (Prozac) radically alter their behavior, endangering their own survival (17). Exposure to pharmaceutical compounds containing hormones has been linked to sex mutations. For instance, in one study, female fish developed male genital organs, sex ratios were skewed in some aquatic populations, and bass produced cells for both sperm and eggs (3). Other documented effects of pharmaceutical exposure include kidney failure in vultures, impaired reproduction in mussels, and inhibited growth in algae (3).
  • Human Health Concerns: In 2008, an Associated Press investigation revealed that pharmaceuticals had been detected in the drinking water supplies of 24 major metropolitan areas serving 46 million Americans; all supplies received water from rivers and reservoirs that contained previously treated wastewater (18, 19). These drinking water supplies contained antibiotics, anti-convulsants, mood stabilizers and sex hormones (20). Scientists and health professionals don’t fully understand the risks from persistent low-level exposure to pharmaceuticals through our drinking water (and potentially our food supply). Experimental research has found that exposure to small amounts of medication affect human embryonic kidney cells, causing them to grow slowly; that human blood cells show biological activity associated with inflammation; and that trace medications can cause human breast cancer cells to proliferate more quickly (21). In studies of soil fertilized with sludge product from wastewater treatment plants, researchers found that earthworms and vegetables had absorbed pharmaceutical compounds, thus posing a potential threat to food chains (3). Studies to date suggest that most found concentrations of pharmaceutical compounds in water systems today (not in lab environments where higher concentrations can be tested) have little known impact to most aquatic species or to humans (22, 23). Nevertheless, preliminary findings such as those above concern some scientists and water treatment experts (13, 23).

Case Study of the South San Francisco Bay

California’s San Francisco Bay and Delta, located at the terminus of the San Joaquin and Sacramento Rivers, is the largest estuary on the west coast and drains almost half the land area of California. PPCPs have been found throughout the Bay’s sediments, plankton, invertebrates, fish, birds, and even marine mammals like seals (24). Both San Jose (25) and Santa Clara (26) are large urban cities that get most of their drinking water from the Sacramento-San Joaquin River Delta to the east of the San Francisco Bay -- water that comes primarily from the Sacramento River (26). The Sacramento River originates over 400 miles to the northeast of the Bay in California’s Sierra Nevada Foothills and winds through many small towns and cities (and their treatment facilities) on its journey to the coast (27). Once in the Silicon Valley (South Bay), the water is mixed with local supplies, treated once more, and piped to residents as drinking water (27). While both San Jose and Santa Clara reported that they had not tested for pharmaceuticals in their drinking water (18), PPCPs were found in the larger watersheds of both cities (28).

Google Earth image of San Francisco Bay

South San Francisco Bay’s largest wastewater treatment plant, the San Jose/Santa Clara Water Pollution Control Plant (WPCP), rests on 2,600 acres on the southernmost banks of the San Francisco Bay (29). Of the three wastewater treatment plants that discharge into the lower South Bay, the San Jose/Santa Clara plant serves the largest population and discharges the most wastewater (30). Wastewater travels to the plant from a 300-square mile area and from eight cities in the Santa Clara Valley. The plant treats the sewage water of 1.4 million people and 16,000 businesses (31). Sixty-two percent of the sewage comes from residential sources, 7 percent is industrial, and 31 percent is from commercial businesses (30). Through 2,200 miles of sewer pipes, the plant receives on average 100 million gallons of raw sewage per day (most wastewater treatment plants receive around 10 million) (31, 32).

Drugs From The Plant:

In July, 2010, the San Jose/Santa Clara WPCP published results from a study that tested wastewater for 166 different compounds, including PPCPs, steroids, hormones, pesticides, flame retardants, and polychlorinated biphenyls (PCBs) (13, 32). Plant and city government staff collected samples of wastewater influent, effluent, and waste solids, and analyzed the samples using U.S. EPA analytical methods to achieve trace-level quantification of contaminant compounds (32). For compounds with a sufficient number of quantified concentrations at more than one sampling point, staff calculated a removal efficiency and mass balance estimate (32). Few studies compare pharmaceutical contamination from an individual plant’s influent (untreated raw sewage) to contamination found in the plant’s effluent (treated wastewater), and this research is unique even internationally according to its authors (13).

Google Earth Image of South San Francisco Bay and Research Sites

Results from the study show that some compounds are reduced significantly by the plant’s current treatment processes (such as 99 percent of ibuprofen), while others are unaffected or even increased (such as fluoxitine – commonly known as Prozac) (32). Many compounds were significantly reduced in the treatment process (between 88 percent to 100 percent reduction in final effluent) (32). Ninety-five of the total 166 contaminants tested were detected in at least some effluent samples; 53 of the detectable 95 were measured at quantifiable levels, and the rest were detected but not quantified (concentrations were too small to be accurately measured) (32). Ten of the quantifiable compounds showed less than 75 percent removal, and for three, the treatment process appeared to have no impact whatsoever (32). Pharmaceutical contaminants that showed what plant operators and study authors qualified as "poor to no reduction" through current treatment processes included those listed below in Table 1.


Drug Type

Influent (ng/L)



% Reduced


Bronchodilator (lung diseases and asthma medication)















Anticonvulsant and mood stabilizer



















Table 1: Table adapted from Dunlavey et. al., 2010, Table 3: "Removal Efficiency and Mass Balance Estimate for Conservative Constituents." Ng/L = nano-gram per liter; a nanogram is one billionth (1/1,000,000,000) of a gram.

Drugs In The Bay:

The South Bay is relatively stagnant; during dry months, the lower South Bay can receive nearly all of its freshwater inflow from the three wastewater treatment plants located along its shores (30). In 2006, the San Francisco Estuary Institute’s "Regional Monitoring Program" sampled and tested for PPCPs in the lower San Francisco Bay (30). This study tested influent and effluent samples from the San Jose/Santa Clara WPCP and another smaller local plant (serving Palo Alto) as well as ambient surface water at multiple points in the lower South Bay at low tide (30) This study also followed the same U.S. EPA methods employed in the San Jose/Santa Clara plant study (30). PPCP concentrations in Bay waters decreased with increased distance into the Bay (and away from the plant); salinity measurements collected along with Bay samples indicated this was the result of dilution through mixing with saline Bay waters (29). The San Francisco Estuary Institute study (published in 2009) evaluated 39 compounds from fourteen different classes of use. Researchers found (similar to the San Jose/Santa Clara Plant’s study) that while some PPCP compounds were not detected or not able to be quantified, several were present in measurable quantities, including those listed in Table 2 below (30).


Drug Type





Bay (ng/L)

EcoToxicity Thresholds



Pain relief medication
















No information provided


Opiate, pain relief medication




No information provided


Psychoactive stimulant




No information provided


Blood pressure medication


















Cholesterol regulation medication
















No information provided

Table 2: Table adapted from Harrold et al. 2009, Table 8: "Average concentrations of PPCPs in influent, effluent, and Bay water samples from Lower South San Francisco Bay…" Ng/L = nano-gram per liter; a nanogram is one billionth (1/1,000,000,000) of a gram.

Test results from a testing station at the outlet of the Artesian Slough (the waterway that channels wastewater directly from the treatment plant to the Bay) show concentrations of pharmaceuticals that were typically higher than those found further out into the Bay. Thus due to location, the presence of these compounds at the outlet of the Artesian Slough can be primarily attributed to effluent coming from the San Jose/Santa Clara plant.

Ecological Impacts

Overall, the San Francisco Estuary Institute study found that pharmaceutical concentrations generally decrease with distance from the treatment plant and that concentrations were generally at levels below accepted toxicity values; however toxicity thresholds for many of the measured compounds are not established (30).  The antibiotic sulfamethoxazole appeared in concentrations two to forty times higher than one known threshold of concern; concentrations of between 44.8 to 1,060 ng/L were observed relative to a 27 ng/L toxicity threshold derived from acute toxicity tests on blue-green algae, an often-used indicator species for toxicity impacts (30). At the same time, sulfamethoxazole concentration levels came in well under the threshold established by another test wherein 30,000 ng/L was found to impact the growth of duckweed (another aquatic plant used regularly used in toxicity studies) (33).

Many PPCPs present in the Bay have been tested for ecological impacts at much higher concentrations than those actually found in the Bay. Through these tests, some compounds were found to have harmful effects. For example, gemfibrozil reduced testosterone in fish, and erythromycin-H2O inhibited the population growth of green algae (30). In other cases, little effect was demonstrated. For instance, extended multi-generational exposure of a freshwater amphipod (a tiny shrimp-like crustacean) to acetaminophen, gemfibrozil, and ibuprofen did not impact survival, mating, body size, or reproduction—common evaluation factors in toxicity studies that demonstrate environmental impact (30).


Available evidence suggests that for most found concentrations of pharmaceutical compounds in water systems today (not in lab environments where higher concentrations can be tested), there is little to no threat to most aquatic species or humans (22, 23). Nevertheless, the increasing number of U.S. government agency efforts to address this topic (see USGS Toxic Substances Hydrology Program "emerging contaminants" project [34], and U.S. EPA’s "PPCP Research Areas" [35]) suggest that scientists are concerned. Undeniably, the increasing manufacture and use of PPCPs has resulted in the introduction of diverse and novel contaminants into water systems in the U.S., and worldwide (36). The prevalence of drugs in waterways begs the question: Are we permanently altering the composition and health of local, regional, and even global water systems? We’ve already seen industrial-era contaminants like mercury do precisely this.


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About the author: Morgan Levy is a graduate student in UC Berkeley’s Energy & Resources Group, researching interdisciplinary water resources issues particular to California and the American West. She recently returned from a Fulbright Fellowship in Environmental Studies – Water Management in The Netherlands, where she interviewed farmers about agricultural water use.