Poisoning the well
Updated: 2018-10-19 06:16
The residues of drugs used for treatment of human illness and for the raising of farm animals have to go somewhere and they're headed straight for
local waters. Honey Tsang reports.
Over the past few years, Deng Wenjing and her colleagues slogged along riversides, on a quest to ascertain just how badly Hong Kong's rivers have been polluted by antibiotics.
The team trekked for miles collecting dozens of water samples from major rivers in Hong Kong. They scooped surface water into amber glass bottles, and then took them gingerly to a laboratory for prompt testing.
Deng is not the first scientist to look into antibiotic pollution in the city's waters. Her research, however, is the most extensive territory-wide survey, providing an overview of the hazards antibiotics are creating in local rivers and streams.
As an environmental scientist, she's been particularly concerned by unused and excreted antibiotics in effluent spewed into river waters every day. Unlike well-documented pollutants like E.coli, plastic and heavy metal, antibiotics are a rather novel pollutant whose actual environmental risk is still not fully understood, said Deng, assistant professor of the Department of Science and Environmental Studies at the Education University of Hong Kong.
"But what we are certain now is that the growing amount of antibiotic residues in waters is bound to lead to increasing drug resistance in bacteria, antimicrobial resistance," she said.
What concerns Deng is also worrying medical and environmental experts worldwide. Drug-resistant bacteria have bred a variety of superbugs. Previously treatable bacteria became more resistant to treatment, with some even becoming incurable. The environmental authority of the United Nations, in 2017, declared that antibiotics set free into the environment are among the greatest emerging challenges to public health.
Most antibiotics eventually are discharged into the aquatic environment sewage channels.
"But what's at issue right now is that Hong Kong's sewage treatment plants are geared only to eliminate conventional pollutants, like organic matter, suspended solids or pathogens, but not antibiotics," Deng stressed.
With that concern in mind, Deng determined to tally up concentrations of antibiotics residues in the water. She started in 2014, hitting 25 sampling sites around the city, then took an entire year to complete lab testing. She narrowed her research to six commonly used antibiotics, and was not surprised to detect all six in the city's rivers.
Among them, ofloxacin (OFL), an antibiotic effective in treating a variety of bacterial infections like pneumonia and urinary tract infections, was most frequently found. OFL had a high detection rate of 69.6 percent and a median concentration of 0.7 nanograms per liter (ng/L).
Compared with rivers on the Chinese mainland, the concentration of OFL in Hong Kong was relatively low. The Yellow River and Pearl River on the mainland were documented with remarkably high amounts of OFL, with their respective highest OFL concentrations recorded at 129 ng/L in 2009 and 108 ng/L in 2011.
Some developed countries and regions also showed alarmingly high OFL concentrations. The Valencia region in Spain had the highest OFL at 4,778 ng/L in 2015, while that of the Seine river in France was at 55 ng/L in 2008.
OFL, under the class of fluoroquinolone antibiotics, is a potent medication in treating tuberculosis, an infectious lung disease transmitted by the airborne bacterium Mycobacterium tuberculosis. The ailment is deemed one of the top 10 causes of death in the world, killing 1.6 million people and afflicting 10 million in 2017. To the disappointment of scientists, the bacterium has already developed resistance to OFL.
Another antibiotic of concern is doxycycline, a medication prescribed to treat infections like typhus fever and respiratory tract infections, as well as acute acne. Its volume in rivers also bears a medium-to-low risk to algae. Its detection rate stood at 30.4 percent, with a median concentration of 17.9 ng/L - a level comparable to rivers in North America, Spain, France and in the Yangtze and Pearl rivers on the Chinese mainland.
Antibiotics in themselves are not harmful by nature, Deng said. Nonetheless, the mis-discharge of it might bring about the emergence and circulation of antibiotic-resistant bacteria, an issue that scientists had never thought about decades ago, she added.
Although antibiotic residues in waters, so far, haven't yet reached hazardous levels, the mere existence of them might suffice to promote selection of resistant genes in bacteria. Those resistant genes could be passed to other environmental bacteria through horizontal gene transfer - the principal mechanism for disseminating antibiotic resistance in the bacterial world.
Reinforce the old-fashioned
Zhang Tong, professor of environmental engineering at the University of Hong Kong, shared the same concerns. He said wastewater treatment plants are always hot spots for horizontal gene transfer, due to their profuse amounts of bacteria and nutrients.
From 2007 to 2011, Zhang conducted a thorough investigation of antibiotic-resistant genes in activated sludge from Shatin Sewage Treatment Works. In the study, he discovered an abundant amount of resistant genes in the samples. The genes resistant to antibiotics aminoglycoside and tetracycline were most frequently detected.
Zhang's findings were contributed to the UN last year, helping to shed light on the impacts antibiotic residues have had on effluent and the environment in general.
When asked about the main sources of the antibiotic wastes in Hong Kong, Zhang said the city's situation is unique. The city has only a small number of pig and poultry ranches and those haven't contributed a significant amount of antibiotics to their surroundings. As of 2017, there were 43 local pig farms and 29 poultry farms in town.
"It's deduced that most antibiotic contaminants in the sewage were from hospitals and households. Hospitals are considered the biggest hot spots as they have large, concentrated amounts of antibiotics prescribed and consumed every day," he added.
In 2016, the total amount of antimicrobials prescribed for patients in public hospitals was 904.4 defined daily doses (DDD) per 1,000 bed days occupied - a 3.4-percent increase from the 874.3 DDD per 1,000 bed days occupied in 2014.
In Hong Kong, public hospitals and clinics have to conform to the law and send unwanted or waste medicine, including injections, to the Chemical Waste Treatment Centre in Tsing Yi for incineration. The incinerator is kept at over 850 C to ensure complete destruction of pharmaceuticals. In 2016, about 695 tons of medication waste from public healthcare facilities was burned off in the incinerator.
"Despite that, we have to note that the human body cannot fully absorb or break down antibiotics," Zhang stressed. "There's a sizeable amount of antibiotics expelled with the excreta of patients, which at the end winds up in wastewater treatment plants and being released to the waters," he added.
In order to minimize the discharge of antimicrobials, Zhang suggests the government set local hospitals as the main target for intervention. One potential measure is to install an individual sewage treatment unit in every public hospital as a preliminary procedure to drastically reduce antibiotic content before channeling to the treatment plants, he added.
The upgrade of the sewage treatment to remove antibiotic residues in effluent should also be placed high on agenda, he added. Sewage treatment is classified into three main stages in order: primary treatment to get rid of solid waste and grit by sieving; secondary biological treatment that decomposes organic matter and nutrients; and tertiary treatment, a mix of physical and biological process to further purify effluent.
Zhang suggested the authority should ramp up efforts to strengthen the tertiary treatment, in which they can tap into membrane bioreactor (MBR) technology, a process combining membrane microfiltration and biological wastewater treatment to filter out even the very fine bio-solids, including antibiotics, from the effluent. This is to minimize antibiotic residues in effluent before they are discharged into rivers. However, he said, the high cost of MBR might one of the factors hindering the advancement.
All ends up in waters
In September this year, Chung Shan-shan, program director of the Master of Science in Environmental and Public Health Management at Hong Kong Baptist University, released a study that showed leachate from landfill sites, liquid that trickles from garbage piles, contained an alarming amount of antibiotic residues.
By studying three local landfill sites between 2015 and 2016, Chung found ciprofloxacin (CIP), an antibiotic used to treat various bacterial infections such as urinary tract infections, was at a disturbing level. Its highest concentration was found in untreated leachates in West New Territories (WENT) Landfill in Tuen Mun, at 3,410 ng/L - 53 times the safety level, that is, the predicted no-effect concentration (PNEC), at 61 ng/L.
Even the treated leachate in WENT Landfill, a less contaminated effluent after removing its sludge and breaking down its organic compounds that flushes directly into Hong Kong waters, had a CIP concentration of 1,259 ng/L, over 20 times the PNEC for CIP.
"A high concentration of antibiotic residues in the environment can lead to antibiotic resistance in bacteria and reverberate along the food chain," said Chung. "It will start from marine creatures, and up along the food chain, and eventually affect human beings."
Echoing Chung's position, Deng added that algae, at the bottom of the food chain in the marine environment, was at risk. In her study, two antibiotics were verified as exerting an ecological risk (from low to medium risk) to this basic species in waters.
"The antibiotic-resistant genes might develop in algae and spread to fishes which feed on them," she said.
It's possible for humans to pick up the genes or even the antibiotic-resistant bacteria by eating seafood. She suggested the public consume more wild fish and less farmed fish. "The large population of cultured fish in a cramped area with only a little mobility is more predisposed to catching antibiotic-resistant genes," she added.
Globally speaking, the vast majority of used antibiotics, or 70 percent, goes into animals. The rest is consumed by the humans, according to UN estimates. Based on those proportions, more antibiotics were discarded by husbandry industry, agriculture and aquaculture than from human usage.
Even though Hong Kong has fewer ranches, she spotted a pattern showing that water samples collected near ranches in the northern regions of the New Territories had a distinctly higher concentration of antibiotic residues. "We suspect the runoff from these farms went directly into the river as the farms are in close proximity to the riverside," she added.
Deng and many other environmental scientists liken antibiotic pollution in the environment to climate change - an issue that has been ignored for decades but is now believed to have caused far-flung and calamitous incidents.
Deng is seeking more resources and funding to conduct a more comprehensive study covering a wider spectrum of antibiotics. Her goal is to map out a fuller picture of antibiotic risks to aquatic environments.
Meanwhile, she calls on the Hong Kong government to keep pace and start monitoring antibiotic residues in effluent regularly. The next move is to launch a "drug take-back program" to collect unused medication from the masses and preclude their fouling the environment.
(HK Edition 10/19/2018 page7)