The Emerging Threat of Antibiotic Residues in the Aquatic Environments of East Africa: A Systematic Review

Abstract

Background:

Antibiotic contamination of aquatic ecosystems, driven by poor waste management, is a critical public and environmental health concern in East Africa, though comprehensive regional data remain limited.

Objectives:

This systematic review synthesizes evidence on the presence, concentration, and impact of antibiotic residues in East African water bodies.

Methods:

A systematic review was conducted in accordance with PRISMA guidelines. PubMed, Scopus, and Google Scholar were searched for studies published between 2010 and 2023 that reported the detection or quantification of antibiotic residues in aquatic environments of East African countries. Data on antibiotic classes, water matrices, detection frequencies, concentration ranges, analytical methods, and limits of detection were extracted and synthesized descriptively.

Results:

Of the 5,551 records identified, 20 studies met inclusion criteria. All eligible studies originated from Kenya (70%), Uganda (20%), and Ethiopia (10%). A total of 49 antibiotics belonging to 11 classes were investigated across wastewater, rivers, lakes, surface water, and groundwater. Antibiotics concentration ranged from 0.0008 to 240 830 μg/l, with the highest levels detected in wastewater effluents. Sulfamethoxazole was the most frequently detected antibiotics (80.36%), followed by norfloxacin and enoxacin. Overall, 73.5% (36/49) of detected antibiotics exceeded 0.1 μg/l, a concentration associated with ecological risk and AMR selection pressure.

Conclusion:

Antibiotic residues are widely present in East African aquatic environments at concentrations that may pose significant ecological and public health risks. Strengthened wastewater treatment, routine environmental monitoring, and regionally coordinated antibiotic stewardship and regulatory measures are urgently needed.

Keywords

systematic review antibiotics residue aquatic ecosystems limit of detection Eastern Africa

Introduction

Active pharmaceutical ingredients (APIs) are the biologically active components in pharmaceutical products that produce the intended therapeutic effect.¹ Globally, around 4000 APIs are used in prescription medicines, over-the-counter (OTC) drugs, and veterinary medications; these may include a wide range of compounds, such as antibiotics.¹ Antibiotics are antibacterial drugs with complex molecular structures that can destroy or cease the bacterial growth.² They are increasingly recognized as a threat to the environment and human health when their residues end up in aquatic environments despite being necessary for human and animal health.^3,4 Thus, antibiotics are the frequently used in human and veterinary and most frequently found as residuals in various aquatic environments.⁵

Antibiotics are classified based on their chemical structure, mode of action, spectrum of activity, and route of administration. Common groups categorized by their mode of action include β-lactams, sulfonamides, monobactams, carbapenems, aminoglycosides, glycopeptides, lincomycin, macrolides, polypeptides, polyenes, rifamycins, tetracyclines, chloramphenicol, quinolones, and fluoroquinolones.^6
-8 Presently, the dangerous issue of these antibiotics contaminating water parts is arising that is supported by various scientific evidences as they have numerous, undeniable negative effects on both the aquatic environment and human health.^6
-8 Widespread antibiotic use contributes significantly to environmental contamination, with households being the primary source, accounting for 96.3% of pharmaceutical residue discharge.^9,10

The global consumption of antibiotics increased from 9.8 Defined Daily Dose (DDD) per 1000 per day to 14.3 DDD per 1000 per day between 2000 and 2018, according to a different study.¹¹ These intentionally or unintentionally consumed antibiotics may accumulate, deposit, or be stored within the cell, tissue, organ, or edible products of the animal as a parent compound or its metabolite.¹² Furthermore, the extensive use of antibiotics for the treatment of infectious diseases across Africa leads to substantial amounts of residual pharmaceuticals, which are ultimately discharged into aquatic environments as active compounds.^13,14 Consequently, the majority of antibiotic molecules (70%-90%) are excreted unchanged through urine and feces to aquatic ecosystem even though a small percentage of them are metabolized in humans or other animals.^15
-17

Antibiotics pollute water in African countries due to improper disposal and misuse, leading to chemical and biological transformations in aquatic environments.^18,19 Antibiotic residues in water can harm aquatic life, cause mutations, and promote drug resistance, threatening ecosystems and human health.^8,13,19,20 Antibiotic resistance, first noted before 1950, has led to rising antimicrobial failures, particularly in developing countries including East Africa.²¹ A more recent investigation discovered that Sub-Saharan Africa (SSA) had the highest cumulative levels of active drug residues in its rivers, with Ethiopia, Tunisia, the Democratic Republic of the Congo, Kenya, and Nigeria ranking first through fifth, respectively.²² Sub-Saharan Africa has the highest AMR burden globally, with projected annual deaths reaching over 4 million in both Africa and Asia.^23,24 If AMR is not controlled, it is anticipated that there will be 10 million deaths globally by 2050, costing the global economy about US$100 trillion.²⁵ In 2014, multi-drug resistant infections caused around 48 000 deaths in the EU and USA. Currently, AMR is linked to 700 000 deaths annually and may cause 10 million deaths per year by 2050, mainly in developing countries. Its economic impact could reduce global GDP by 2%–3.5%, costing up to $100 trillion by 2050.²³

Many investigations throughout the world have been established that the existence of antibiotics as emerging pollutants in the aquatic environment; however, sources of the majority of these reports are outside Africa.¹³ Moreover, despite it was believed that Africa had the highest number of reports of antibiotic resistance (AR), and that South-East Asia and Africa together accounted for 45% of AR-related deaths, the data for this report, came from publications of just a few African countries which implies that there is limitation of studies and scarcity of compiled information about antibiotics residues particularly in east Africa.²⁶ On the other hand, antibiotic usage policies, population densities, and chemical characteristics of the antibiotics can all have an impact on the presence and distribution of antibiotics in water bodies.²⁷

Thus, understanding the extent and distribution of antibiotic residues in aquatic environments will aid in evaluating potential ecological risks and formulating mitigation strategies by developing policies and regulations for the use, monitoring, and disposal of antibiotic residues.²⁸ This review provides scientific evidence to support antimicrobial stewardship by highlighting the presence of antibiotic residues in East Africa’s aquatic environments. It emphasizes the need for regional cooperation and knowledge sharing to tackle the environmental and health impacts of these residues.²⁹ This systematic review is essential for mapping the effects of antibiotic residues on marine ecosystems and laying the groundwork for regular monitoring programs that address environmental risk and control strategies in the aquatic environment of east Africa. The current systematic review was carried out by considering 3 specific review questions outlined in the systematic review reporting forms protocol. These questions include: (1) what is the frequency of antibiotic residue discovered in aquatic settings? (2) Which aquatic setting exhibits the highest occurrence of antibiotic residue? (3) What types of antibiotics are present in significant quantities across various aquatic environments?

Material, and Methods

Study Protocol, and Literature Search Strategy

The PubMed, Google Scholar and Scopus databases were used as sources of information to find published articles related to the present study. Antibiotic residue, Water and East Africa were the key search terms used in this review. This systemic review was performed to assess the antibiotics residues in aquatic environment of east Africa countries (Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, South Sudan, Sudan, Tanzania, and Uganda). Articles were searched for 5 days; September 01-06/2023. Keywords were combined by Boolean operators (AND, OR); as ((Antibiotic OR Antimicrobial OR Pharmaceutical OR Medicine OR Drug OR “Antibiotic residue” OR “Antimicrobial residue” OR “Pharmaceutical residue” OR “Antibiotics detection” OR “Antibiotics level” OR “Antibiotics occurrence”) AND (Water OR Pond OR Ocean OR River OR Lake OR “Stream water” OR “Ground water” OR “Surface water” OR Wastewater OR Freshwater OR “Drink water” OR Sewage OR Marine OR aqueous) AND (“East Africa” OR Burundi OR Djibouti OR Eritrea OR Ethiopia OR Kenya OR Rwanda OR Somalia OR “South Sudan” OR Sudan OR Tanzania OR Uganda)). The steps recommended in the guideline of Preferred Reporting Items for Systematic reviews and Meta Analyses (PRISMA) was followed for reporting the results of this systematic review.³⁰ The PRISMA checklist was prepared in accordance with the systematic review protocol, which guided our review process, including the search strategy, critical appraisal of included studies, narrative synthesis, and evaluation of the confidence in the evidence based on predefined criteria (S1File 1).

Inclusion and Exclusion Criteria

To ensure that only relevant works were included in this systematic review, studies meeting the following criteria were selected: published literature written in English, conducted in 1 or more East African countries, accessible as free full-text versions online, published between 2010 and 2023, and containing data on at least 1 antibiotic residue in water. Studies were included if deemed eligible based on their titles and/or abstracts. Studies excluded from the review were reports, gray literature, editorials, and articles that did not focus on water samples. Studies published prior to 2010 were excluded because methodological capabilities for reliably detecting antibiotic residues in water bodies were limited, and to ensure the inclusion of the most recent and relevant data on antibiotic residues in aquatic ecosystems in East Africa.

Data Extraction Process

Articles retrieved from PubMed, Scopus, and Google Scholar using predefined search terms were initially screened based on their titles and abstracts. Those that met the inclusion criteria were exported and organized into a dedicated collection folder in Zotero. The full texts of eligible articles were then thoroughly reviewed by experienced authors, with any disagreements resolved through discussion. Data extraction focused on key study parameters, including the study country, sample source, collection period, extraction method, analytical techniques, and number of studies included as well as reported detection frequencies. Three experts meticulously reviewed all included articles to ensure accuracy. Antibiotic levels detected in various aquatic environmental samples including groundwater, rivers, surface water, wastewater (effluents or influents), and lakes were systematically extracted. To minimize missing data and bias, multiple independent searches were conducted by different researchers.

Data Synthesis and Statistical Analysis

Data extracted from eligible sources were compiled in an Excel spreadsheet version 10 and analyzed using SPSS (version 26). After synthesis, critical parameters including the total sample examined, total sample positive, detection frequency, percentage detection frequency, limit of detection (LOD), and LOD for respective antibiotics—were considered. The results were presented in tables and supplemented with a narrative description of the evidence captured from published scientific studies.

Results

Initially, 5551 publications were accessed from 3 electronic databases (PubMed, Scopus and Google scholar). From these 681 results were removed using Mendeley citation manager due to duplication. Four thousand eight hundred seventy studies were screened and 4631 of them were excluded by their titles and abstracts. Studies assessed for eligibility were 239 from which 219 were found ineligible.^31
-50 Finally, 20 studies were included in this review following PRISMA ﬂow diagram (Figure 1).

Figure 1.

PRISMA flow diagram that shows the search and selection of included studies.

Selection and Characteristics of Eligible Studies

From the east African countries 14 articles out of 20 included studies were found from Kenya which covers 70% of included articles. The other 6 articles were from Uganda (20%) and Ethiopia (10%). Consequently, the literatures found only from those 3 countries were reviewed and analyzed since no studies were found in other east African countries. Most of the reviewed studies (40%) were published in 2020. The water parts assessed in this review article were groundwater, surface water, rivers, lakes, and wastewater. The concentrations of antibiotics detected in wastewater ranges from 0.002 to 240 830 μg/l; lakes 0.8-5.6μg/L; rivers 0.08 to 506 μg/l and groundwater 0.0055-2.34 μg/L.

The analytical methods used in the reviewed literatures were Liquid Chromatography-Mass Spectrometry (LC-MS/MS), Liquid Chromatography Coupled to High Resolution Mass Spectrometry (LC-HRMS), Quadrupole-Time-Of- Flight (QTOF), Ultra-High Performance Liquid Chromatography (UHPLC), and Ultra-Performance Liquid Chromatography (UPLC). From those analytical methods Liquid chromatography with mass spectrometric detection has been effectively used in determination of many classes of APIs in water samples.

Sample extraction methods used were Solid Phase Extraction (SPE) in 12 studies (60%), Liquid/Liquid Extraction (LLE) and Oasis HLB cartridges even though 4 studies were not mentioned the sample extraction method used. Sample collection period was covered both in dry and wet seasons to know effects of water increment on the samples. The detail about sample information, sampling period, number of antibiotics studied in each article, extraction and detection methods used reported in the retrieved articles were addressed in Table 1.

Table 1.

Sample Information, Sampling Period, Extraction and Detection Methods Reported in the Retrieved Articles.

Country	Place of Study	Sample	Sample collection period	Sample extraction method	Analytical methods used	Ref.
Kenya	Kisumu County	Groundwater	February 9th and 15th, 2021	SPE	LC-MS/MS	Karimi et al³⁷
	Sosiani (Uasin Gishu County)	Surface water (River)	June, 2020 and February, 2021	SPE	HPLC, LC–MS/MS	Chemtai et al³²
	Lake Victoria South Basin	Surface water (Lake)	September and October 2017	NA	LC-HRMS	Kandie et al³⁶
	Machakos town	Wastewater Surface water	January and September 2019	NA	LC-ESI-MS/MS.	Kairigo et al³⁴
	Machakos, Nyeri and Meru	Wastewater (influents, effluents), Surface water	January 2019	Oasis HLB cartridges and SPE	LC-ESI-MS/MS	Kairigo et al³⁵
	Nairobi/Athi	River	March, 2019	NA	HPLC-MS/MS	Bagnis et al³¹
	Juja, Kiambu County	River	August 2019	SPE	LC-MS/MS	Muriuki et al⁴⁴
	Nairobi, Mbagathi, and Ngong	Hospital wastewater, Surface water	February 2018	SPE	LC/MS/MS	Ngigi et al⁴⁶
	Ngong river	River	Dry and wet season	LLE	HPLC-UV/VIS	Opanga⁴⁸
	Nzoia Basin	Wastewater, River	August–September 2015 and May 2016	SPE, Oasis HLB	UHPLC-HROMS	K’oreje et al⁴¹
	Nairobi County	Wastewater	3 d during two dry seasons in the year for 3 y	SPE	HPLC	Mathenge et al⁴²
	Lake Victoria Basin	Wastewater	October 2014 to September 2015	SPE	HPLC	Kimosop et al³⁹
	Mathare, Ngong, Nairobi, Athi Dandora WSPs, JKUAT WSPs	River, Wastewater	October 2014	SPE	LC-ESI-MS/MS.	Ngumba et al⁴⁷
	Nairobi, Kisumu	Wastewater, Rivers, Groundwater	September 2012 & July 2013	SPE	LC-MS	K’oreje et al⁴¹
Uganda	Lake Victoria	Lake	July to September 2018	SPE	HPLC-LC/MS/MS	Nantaba et al⁴⁵
	Kampala (Nakivubo wetland area and Inner Murchison Bay, Lake Victoria)	Wastewater, surface water and lake water	29 April and 5 May	Oasis HLB cartridges and SPE	UPLC and QTOF-MS	Dalahmeh et al³³
	Kampala	Wastewater (Effluents)	27 March to 13 April 2021	SPE	LC-MS	Kayiwa et al³⁸
	Bwaise and Wobulenzi	Groundwater	(April and May 2018) and (July and August 2020)	SPE	UHPLC LC/MS/MS	Twinomucunguzi et al⁵⁰
Ethiopia	Addis Ababa, (Akaki River)	River Hospital- Wastewater ASTP (Influent, Effluent)	September 2019	SPE	HPLC-DAD	Tegegne et al⁴⁹
Ethiopia	Tikur Anbessa Specialized Referral Hospital	Hospital wastewater	February to June 2018		HPLC	Mesenbet et al⁴³

LC-MS/MS, Liquid Chromatography-Mass Spectrometry; LC-HRMS, Liquid Chromatography Coupled to High Resolution Mass Spectrometry; QTOF, Quadrupole-Time-Of- Flight; UHPLC, Ultra-High Performance Liquid Chromatography; UPLC, Ultra-Performance Liquid Chromatography; SPE, Solid Phase Extraction; LLE, Liquid/Liquid Extraction; NA, Not-Available.

Country-Wise Analysis of Individual Antibiotic Residues in Aquatic Environments: Detection and Quantification Methods

The review provides a detailed analysis of individual antibiotics, examining their sample sources, the number of samples, detection frequency, limit of detection (LOD), and limit of quantification (LOQ) across various aquatic environments in different countries. It was found that sulfamethoxazole was detected in nearly 100% of samples from lakes, wastewater, surface water, and rivers, as reported in studies from Kenya and Uganda. The review also identifies the countries from which the data was sourced (S2File2). In Supplemental Table 2, countries where antibiotic residues have been found need to be incorporated to ensure that geographical locations of these studies are provided to make sure there is sufficient geographic context. For example, SMX was identified in groundwater in Kenya (14.3% detection, 12.7-258.2 ng/L) and surface water (47.4% detection, 1.09-247.0 μg/L), but not in wastewater effluent and lakes of Uganda (38.5%, 1.37-57.96 mg/L, and 100%, 0.8-5600 ng/L, respectively), while TMP has been detected at a 100% rate in Kenyan rivers (0.17-67.32 μg/L), while only 40% was detected in Ethiopian ASTP influent (0.5 μg/l), and CIP was detected at 21% in Ugandan groundwater (340 ng/l) and 100% in Kenyan surface water (13.68-56.02 μg/L). Different units of measurement, including ng/L, go/L, and mg/L, were used to assess antibiotic concentrations, while detection frequencies were expressed as percentages. Some articles provided standards alongside LOD and LOQ, while those that did not were marked as “NA” (Not Available).

Prevalence of Antibiotic Residue in the Study Area

This systematic review was addressed about detection and quantification of 49 antibiotics from 11 classes and 1 not classified were reviewed from various articles regarding their detection and quantification in the marine environment in different eastern African water parts. Antibiotics from Sulphonamide, Penicillin, Fluoroquinolone, Macrolide, Lacosamide, Aminocyclitol, Nitroimidazole, Diaminopyrimidine, Sulfone, Tetracycline, Cephalosporin and Chloramphenicol classes were reviewed for detection frequency and concentrations at which they were detected. About 23 antibiotics were found only from a single article and their detection frequency and concentration were analyzed directly based on that article while others were analyzed from more than 2 articles such as Ciprofloxacin from 13 different articles, Trimethoprim from 16 different articles and Sulfamethoxazole from 17 different articles. The percentage detections were done based on number of articles in which they studied. Concentration ranges were also taken accordingly.

Overall analysis in this review indicates that 9 antibiotics like Sulphaguanidine, Sulfamonomethoxine, Sulfamerazine, Sulfachlorpyridazine, Sulfadimethoxine, Sulfaquinoxaline, Sparfloxacin, Rothithromycin, Dapsone were not detected in any water parts reviewed from all the articles. Oppositely, 12 antibiotics were most frequently detected in aquatic environment with >80% percentage detection frequency (DF) such as Sulfamethoxypyridazine, Sulfsoxazole, Sulfamethizole, Sulfapyridine, Sulfacetamide, Penicillin V, Oxacillin, Spiramycin and Spectinomycin (100% DF), Norfloxacin (89% DF), Enoxacin (88% DF), and Sulfamethoxazole (80.4% DF). On the other hand, 9 antibiotics such as Sulfadoxine, Amoxicillin, Nafcillin, Ampicillin, Ciprofloxacin, Levofloxacin, Metronidazole, Trimethoprim, and Tetracycline were less frequently occurred in different water parts with the detection percentage from 50% to 80%.

Other 18 antibiotics were occasionally detected in aquatic environment with <50% percentage of detection. But the detection frequency of Cefotaxime was not available. The concentrations of antibiotics assessed in this review ranges from 0.0008 μg/l (that of Sulfamethoxazole and Sulfacetamide both from lakes) to 240 830 μg/l (that of Clarithromycin from wastewaters). Three antibiotics were quantified in highest concentration. Clarithromycin (240 830 μg/l), Sulfamethoxazole (57 960 μg/l), and Cefotaxime (17 000 μg/l) all from wastewater effluents. The first 2 antibiotics with highest concentrations were obtained from Uganda wastewater while the third higher (Cefotaxime) concentration was obtained from the Hospital wastewater in Ethiopia. Detail of these information about antibiotics regarding their generic name, their abbreviations, sources from which they obtained, their detection status, quantification status and their respective classes based on mode of action were summarized in Table 2.

Table 2.

Overall Generic Name of Antibiotics, Their Abbreviations, Sources From Which They Obtained Their Detection Status, Quantification Status and Their Respective Classes.

Antibiotics	Abbreviation	Total Samples	Number of articles assessed the antibiotic	Percentage (%) of detected antibiotics combined from all reviewed articles	Overall concentration range of antibiotics in (μg/L)	Antibiotic class
Sulfamethoxazole	SMX	504	17	80.36	0.0008-57 960	Sulfonamide
Sulfaguanidine	SFG	10	1	0	0
Sulfamonomethoxine	SMM	10	1	0	0
Sulfachlorpyridazine	SCP	26	2	0	0
Sulfadimethoxine	SDMX	10	1	100	1.61-3.69 μg/L
Sulfadiazine	SDZ	52	3	10.93	0.08-3.69
Sulfamethazine	SMZ	268	5	32.91	0.0024-23.64
Sulfadoxine	SDX	193	4	58.03	0.09-5
Sulfathiazole	STZ	58	2	23.33	0.14-7.38
Sulfamethoxypyridazine	SMPZ	10	1	100	0.33-1.23
Sulfisoxazole	SXZ	10	1	100	2.47-5.95
Sulfamethizole	SMTZ	10	1	100	0.7-1.13
Sulfapyridine	SPD	10	1	100	2.45-6.57
Sulfaquinoxaline	SFQ	10	1	0	0
Sulfamerazine	SMR	16	1	0	0
Sulfanilamide	SFM	16	1	43.75	0.36-7.7
Sulfacetamide	SFA	75	1	100	0.0008-0.013
Penicillin V	PEV	10	1	100	2.89-4.86	Penicillin
Amoxicillin	AMX	65	6	52.31	0.05-9.7
Cloxacillin	CLX	51	3	21.57	2.14-10.37
Nafcillin	NAF	26	2	65.38	0.13-3.99
Ampicillin	AMP	74	4	56.12	0.0055-1.35
Penicillin G	PEG	74	3	32.57	0.46-3.74
Dicloxacillin	DCX	60	4	43.33	0.02-8.03
Oxacillin	OXA	16	1	100	0.1-0.21
Norfloxacin	NOR	129	6	88.77	0.1-52.6	Fluoroquinolone
Ciprofloxacin	CIP	314	13	63.38	0.002-1230
Enrofloxacin	ENR	84	3	23.81	0.0143-29.73
Enoxacin	ENX	75	1	88.00	0.0059-0.051
Sparfloxacin	SPX	75	1	0	0
Nalixic acid	NDA	215	3	21.40	0.01-0.1
Levofloxacin	LEV	146	3	71.92	0.0018-3
Azithromycin	AZT	75	1	20.00	0.014-0.06	Macrolide
Erythromycin	ERY	127	4	22.05	0.01-6.73
Rothithromycin	RTM	75	1	0	0
Tylosin	TYL	36	2	27.78	5.46-9.08
Spiramycin	SPI	16	1	100	0.15-1.64
Clarithromycin	CLM	148	3	26.35	0.005-240 830
Lincomycin	LIN	36	2	41.67	3.67-7.77	Lincosamide
Spectinomycin	SPC	16	1	100	0.15-0.7	Aminocyclitol
Metronidazole	MET	293	6	56.31	0.002-5.56	Nitroimidazole
Trimethoprim	TMP	493	16	62.26	1.1-479	Diaminopyrimidine
Dapsone	DPS	10	1	0	0	Sulfone
Tetracycline	TTC	165	4	50.91	0.0027-0.2793	Tetracycline
Metacycline	MTC	48	1	10.42	0.0103
Oxytetracycline	OTC	149	3	49.66	0.017-2.34
Chlortetracycline	CTC	48	1	27.08	0.62
Cefotaxime	CFT	4	1	NA	17 000	Cephalosporin
Chloramphenicol	CAP	134	3	10.45	0.05-0.2	Not classified

Discussion

Antibiotics are critical class of drugs in diagnosis, cure, and treating diseases within the healthcare industry; nevertheless, the misuse of antibiotics has led to a rise in antibiotic resistance, impacting healthcare services.^51,52 Improperly disposing of antibiotics into aquatic environments contributes to the development of antibiotic resistance, posing a significant global risk to public health.^53,54 The concentration of antibiotics from various effluents enters water bodies, which frequently dilute as they go downstream and experience a variety of reactive biotic and abiotic actions.¹⁸ The common entry routes of antibiotics residues into the water parts are excretions after use, irrational disposal of unused antibiotics and waste discharged after their production.⁶

The review found that antibiotic residues were highest in wastewater (0.002-240 830 μg/l), followed by rivers (0.08-506 μg/l), lakes (0.8-5.6 μg/L), and groundwater (0.0055-2.34 μg/L). The wastewater concentrations were comparable to those reported in Tunisia (ng/L to ng/mL).¹³ But this concentration was significantly greater than concentration of the antibiotics studied in wastewaters ranging from low ng/L to 12.7 μ/L.² Moreover, a research article published in 2023, which examined the incidence and distribution of antibiotics in water, revealed that antibiotics were detected in aqueous environments at levels varying from less than 1 nanogram per liter to 100 µg per liter.⁵⁵ Consequently, antibiotic-contaminated wastewater effluents diminish the possibility for treating bacterial diseases by promoting the growth of resistant bacteria and posing a significant toxicity risk to non-target organisms in the aquatic environment.² In addition to encouraging microbial resistance, antibiotic residues can be taken by plants, potentially interfere with physiological processes and perhaps have ecotoxicological effects.⁵⁶ The massive discharge of antibiotic residues into the river can make it inadequate for drinking purposes by polluting it. Additionally, it poses a chronic risk to humans, animals, and aquatic organisms and can vanquish many species of microorganisms by altering their structure.⁵⁷

Evidence showed that, antibiotics residues can enter marine environments, rivers, and lakes and endanger ecology and human health which is considered as emerging global concern.⁵⁵ The sulfonamides, Tetracycline, Beta-lactams, and Macrolides are among the antibiotics that are frequently discovered in water resources around the world.⁵⁸ Similarly antibiotics like Sulfonamide, Penicillin, Fluoroquinolone, Macrolide, Lincosamide, Aminocyclitol, Nitroimidazole, Diaminopyrimidine, Sulfone were also discovered.⁵⁹ Evidence revealed widely used antibiotics particularly macrolide antibiotics, they are frequently found in aquatic settings, which has an impact on ecological health and water quality.⁶⁰ The most contaminated water bodies were the receiving waters of wastewater treatment plants (WWTPs) and highly populated areas. Additionally, the pollution sources led to an identification of macrolides at mean concentrations of up to 3847 ng/l.⁶⁰ Except Rothithromycin, all 5 macrolides (Azithromycin, Erythromycin, Tylosin, Spiramycin, and Clarithromycin) were occurred at concentration that have deleterious to aquatic ecosystem in this study. Of all the antibiotics investigated, clarithromycin stands out the most for misuse; it was found to be present in wastewater effluents at the greatest residual amounts and was classified as a high-risk product to the aquatic environment (PEC/PNEC>7).⁹

Apart, clarithromycin was detected in aquatic environment at the highest concentration of all addressed antibiotics. In general, the presence of macrolides (including clarithromycin) in an aquatic environment can affect cyanobacteria and green algae by changing the natural food webs and preventing cyanobacteria from providing vital ecosystem services.⁶¹ Sulfonamides, abbreviated SAs, are highly consumed and persistent in the environment, resulting in an ecological hazard in aquatic environments where their concentrations range from ng/L to μg/L.⁶² Sulfamethoxazole was the most often accumulating antibiotics from sulfonamide class in aquatic habitats which examined from 17 distinct studies, with an 80.36% detection frequency and concentration ranging from 0.0008 (in a lake) to 57 960 μg/l (in wastewater) in East Africa according to results of this review. Likewise, this antibiotic has been extensively studied in aquatic environments, including surface water, and has been found in 96% of analyses conducted in international studies. It has also been found in Africa (with 8 reports from 4 different countries, with concentrations ranging from 0.00027 to 39 g/l). For instance, Sulfamethoxazole (SMX) was found to have a detection frequency of >85%, accounting for 58% of the antibiotics detected in surface waters ranging from 0.1 to 6.84 g/l, according to a study done in the African country.^6,13,46,63

On the other hand, Trimethoprim, which is combined with sulfamethoxazole to avoid development of resistant bacteria that can be happened with single sulfamethoxazole, has been regularly found in aquatic environments like at 0.4 g/l in surface water as per 2016 according to Olarinmoye et al (2016). The information obtained from routine ecotoxicity bioassays indicated that fish and crustaceans were the aquatic living things with the high susceptibility to the antibiotics sulfonamide following Algae which were the most susceptible. Certain antibiotics, including sulfadiazine (SDZ), sulfamethoxazole (SMX), and sulfamethazine (SMZ), appear to be very dangerous for the aquatic system, according to the risk data.⁶² The current review indicates that more research is required to determine the ecotoxicity of antibiotic combinations including Sulfonamides to marine environments in east Africa.

β-Lactams are the most commonly used class of antibiotics even though resistance to them is concerning issue associated with β-lactamase enzymes produced by bacteria that hydrolyze the β-lactam ring of the drugs and thereby inactivate them.⁶⁴ Penicillin and cephalosporins are group Beta-lactam antibiotics. Penicillin is an antibiotic that breaks down quickly in the environment due to the presence of beta-lactam rings in their structure.⁶ For this reason maximum concentration of Penicillin class antibiotics quantified in this study was 10.37 μg/l (cloxacillin) followed by amoxicillin (0.05-9.7 μg/L)of all 8 Penicillin antibiotics reviewed in this study). However, Penicillin associated environmental toxicity is rare if compared to that of fluoroquinolones, sulfonamide and macrolides. On the other hand, cephalosporin antibiotics used by humans and animals have been regarded as water pollutants because of their extensive presence in aquatic environments.⁶⁵ It has showed a gradual rise in antibiotic resistance from 46% in 2007 to 68% in 2014 in South Africa as reported by different sources including United Nations (UN).¹³ A study in the Netherlands found widespread antibiotic resistance genes in wild birds, particularly aquatic species like waterfowl, gulls, and waders, posing a risk of transmission to humans and livestock.⁶⁶

Fluoroquinolones antibiotics are derived from quinolones and have a broad spectrum activity against gram-negative bacteria through the inhibition of DNA gyrase.¹³ On the other hand, it is more stable and can persist in the environment for longer, spread further, and eventually accumulate to higher concentrations.¹⁵ Seven fluoroquinolone antibiotics were reported, with 4 exceeding 1 μg/l in East African aquatic environments. Ciprofloxacin (1230 μg/l, 63.37% detection), Norfloxacin (52.6 μg/l), Enrofloxacin (29.73 μg/l), and Levofloxacin (3 μg/l) were detected. Ciprofloxacin, first reported in water samples by Olaitan et al (2020) in Nigeria, may impact marine organisms’ growth, reproduction, and liver health.⁶⁷ Moreover, it showed gradual rise in antibiotic resistance from 31% in 2007 to 46% in 2014 with levels from 0.0002 to 15 g/L in South Africa as reported by UN.¹³ Zebrafish named Danio rerio showed a significant decrease in heart rate been exposed to higher concentrations of CIP.⁶⁸ Levofloxacin (LEV), on the other hand, has received the least attention, appearing in only 4% of analyses.^6,69 Similarly, 3 out of 4 antibiotics in Tetracycline group like Tetracycline (0.2793), Oxytetracycline (2.34), and Chlortetracycline (0.62) were detected in aquatic environment at concentration that reduces fish immune system in this study. All of these high-level quantities of antibiotics were occurred in groundwater. Water containing 6.90 mg/l of Enrofloxacin and Levofloxacin for 12 days cause significant inhibition on survival rate of Daphnia magna⁷⁰ even though their concentration in this article was much lower than the provided information. Collectively, fluoroquinolones antibiotics are the most hazardous to aquatic ecosystem due to the accumulation of nitrite and nitrogen oxide as a result of potential nitrification and denitrification processes in aquatic environments.^71,72 It also have an impact on the growth and development of aquatic plants and algae by disrupting their thylakoid membrane and have an influence on antioxidant defense system, growth and development, behavior, and genetic integrity of aquatic animals.⁷³ High concentrations of ciprofloxacin (185 μg/l), norfloxacin (703 μg/l), and lomefloxacin (159 μg/l) were persistently detected in pharmaceutical and hospital wastewater effluents, posing risks of acute mortality and chronic effects on aquatic organisms.⁷⁴

Tetracycline is a widely prescribed antibiotic both for human and animal because of its broad-spectrum activity, effectiveness, and affordability. This class of antibiotics cannot be completely absorbed and metabolized in the body and roughly about 75% is excreted in its parenteral form.^75
-77 Furthermore, approximately about 80% of tetracycline is used in aquaculture for fish feeding as a growth promoter.^78,79 This causes their accumulation in aquatic environment, causing toxicity on microbial community, facilitating the development and spread of antibiotic resistance, polluting drinking and irrigation water, and disrupting microbial flora and aquatic ecosystem.⁶⁹ Moreover in similar to fluoroquinolones, tetracyclines are more stable, can persist in the environment for longer, spread further, and eventually accumulate to higher concentrations.¹⁵ One of the effects of tetracycline accumulation in aquatic environments is reduction of the fish immune system at concentrations of 0.1 to 50 μg/l (at 0.4 mg/ml)¹³ results in zebrafish death), and inhibition of various algal growth at concentration of 0.25-30 mg/l.⁶⁹ Three out of 4 tetracycline antibiotics—tetracycline (0.2793 μg/l), oxytetracycline (2.34 μg/l), and chlortetracycline (0.62 μg/l)—were detected in East African aquatic environments at levels that may weaken fish immune systems. However, their concentrations were too low to harm algae. The high levels found in groundwater may contribute to the spread of antibiotic resistance⁸⁰ in groundwater which in further cause impacts on human beings because of groundwater is widely used. The occurrence and levels of antibiotic residues in the water are varied by season and site over the 3-year period.⁷² Antibiotic residues were higher in aquatic environments during the dry season compared to the wet season due to reduced dilution. This review supports the finding, with the highest concentrations detected in the dry season: Cefotaxime (17 000 μg/l) from Ethiopian hospital wastewater (Feb–June 2018) and Clarithromycin (240 830 μg/l) and Sulfamethoxazole (57,960 μg/l) from Ugandan wastewater effluents (March–April 2021).

Antibiotics residue determination in different water samples can be done by diverse chromatographic methods, such as High Performance Liquid Chromatography-Ultraviolet (HPLC-UV),⁷¹ High Performance Liquid Chromatography-Diode Array Detection (HPLC-DAD), Liquid Chromatography-Mass Spectrometry (LC-MS), Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC- MS/MS)^60,81and Gas Chromatography-Mass Spectrometry (GC–MS).⁸² Also, in this review different chromatographic detection techniques such as HPLC–UV, HPLC–PDA and LC–MS HPLC methods were widely used for determining antibiotic residues in aquatic environments using various detection systems, because of their high selectivity, sensitivity, and ease of sample treatment. In similar way, various qualification and quantification for extraction of antibiotics residues were carried out by using HPLC, UPLC and LC-MS/MS.⁸³ Antibiotics have been extracted from water matrices using extraction techniques like solid phase extraction (SPE) and liquid-liquid extraction (LLE). But salting-out assisted liquid-liquid extraction (SALLE), which relies on the phase separation of water-miscible organic solvents from the aqueous solutions in the presence of high concentrations of salts and uses water-miscible organic solvents that typically have low toxicity as the extracts and use of salts causes almost no environmental pollution,⁶ was not used for sample extraction in entire of studies included in this review.

As analytical methods used to detect and quantify antibiotics residues in Europe’s water bodies implies, the concentrations between 0.019 and 0.089 µg/l have no direct effects on aquatic organisms like algae, crustacean and fish.⁸⁴ However, antibiotic levels of 0.1 μg/l and more in hotspots can cause local environmental antibiotic resistance in microorganisms.⁸⁵ Out of 49 antibiotics studied, 36 (73.5%) were found at concentrations above 0.1 μg/l, posing significant risks to aquatic ecosystems and human health. In contrast, 13 antibiotics were detected below this threshold, with no expected direct effects on aquatic organisms.

Furthermore, as some investigations estimates, the global annual use of antibiotics to be between 100 000 and 200 000 tons; it’s use rose by 65% between 2000 and 2015, and was expected to climb by 200% by 2030.^77,86
-88 In parallel to this, the higher concentration of antibiotics residues can be discharged into water parts which are the global concern particularly in developing countries like east Africa. One of the effect of this is the occurrence of resistant bacteria, even at minute concentrations of antibiotics residues below inhibition limit since it puts pressure on the bacterial population.⁸⁹ For instance, approximately about 90% of bacteria in the marine environment are resistant to at least 1 antibiotic and 20% are multi drug resistant.⁹⁰ The study about presence of antimicrobials and their corresponding ARGs in the sediments of the Awash River Basin,²⁷ Ethiopia also implied the emergence of antibiotic-resistant microbes and eco-toxic effects.⁴⁶ It is also predicted that AMR costs the EU €1.5 billion annually in healthcare values and productivity wastages.⁹¹ The limitation of the articles searched for this review was the absence of published reports on the occurrence of antibiotic residues in aquatic environments in east African countries except Kenya, Uganda, and Ethiopia. Similar to this, reports on the use of antibiotics worldwide with a view toward Africa have been documented, with detailed data on consumption from only Kenya.⁶

Collectively, frequent detection and high concentrations of antibiotic residues in various water parts, especially in eastern Africa.^5,13 This leads to the emergence and development of antibiotic resistance, which will have serious impacts on both human and animal health, disruption of marine ecosystems like fish, amphibians, and invertebrates, contamination of food, drinking, and recreational water, consumer concerns about the use of antibiotics, and disturbances of international trade, which may affect the economy of this area.^{5
-7,10,13,26,67,92}

Strengths, and Limitations of the Study

This systematic review provides a comprehensive analysis of antibiotic residues in aquatic environments across East African regions. A key strength of the study lies in its detailed data synthesis, which consolidates findings from peer-reviewed journal articles, offering a broad perspective on the issue of antibiotic contamination. The study critically evaluates antibiotic pollution across various water bodies, including wastewater, rivers, lakes, and groundwater, highlighting its extent and potential ecological risks. Additionally, the review follows a structured methodology with well-defined inclusion criteria, aligning with the PRISMA framework to ensure transparency and reproducibility. Another notable strength is its relevance to policymakers, as the findings contribute to evidence-based decision-making for environmental regulations and antibiotic stewardship programs.

However, the study has certain limitations. A critical drawback is the scarcity of data from some East African regions, as most of the reviewed studies originated from Kenya, Uganda, and Ethiopia, limiting the generalizability of the findings to the entire region. Additionally, variations in analytical techniques and detection limits among the included studies may introduce inconsistencies in reported antibiotic concentrations, potentially affecting comparative analyses. Another limitation is the lack of standardized methodologies across studies, which may hinder the reliability of cross-study comparisons. Furthermore, while the paper presents valuable data on antibiotic residues, it does not explore in depth the impact of these contaminants on specific aquatic organisms or public health, which could have further strengthened its findings. Despite these limitations, the study provides a critical foundation for future research and policy interventions aimed at mitigating antibiotic contamination in East African water systems.

Conclusion, and Future Needs

This systematic review indicates the widespread presence of antibiotic residues in aquatic environments across East Africa, stressing the urgent need for effective management strategies to mitigate their ecological and public health risks. The findings indicate that hospital and pharmaceutical wastewater contribute significantly to the contamination, potentially accelerating antimicrobial resistance (AMR) and disrupting aquatic ecosystems. Given the high detection rates and concentrations of antibiotics, there is a critical need for stricter regulatory measures, improved wastewater treatment technologies, and systematic monitoring programs. Future research should focus on developing accurate ecological risk assessment models, and evaluating the combined toxicity of antibiotic mixtures. Additionally, raising public awareness about the consequences of antibiotic misuse and strengthening antibiotic stewardship programs will be essential in reducing environmental contamination. The review also suggests, collaborative efforts among policymakers, healthcare professionals, environmental agencies, and researchers are necessary to establish sustainable solutions for controlling antibiotic pollution in East African water bodies.

Supplemental Material

sj-docx-1-ehi-10.1177_11786302261454781 – Supplemental material for The Emerging Threat of Antibiotic Residues in the Aquatic Environments of East Africa: A Systematic Review

Supplemental material, sj-docx-1-ehi-10.1177_11786302261454781 for The Emerging Threat of Antibiotic Residues in the Aquatic Environments of East Africa: A Systematic Review by Duressa Dedefo, Gemmechu Hasen, Belachew Umeta, Desta Assefa, Yesuneh Tefera Mekasha, Simon Genet, Daniel Legese Achalu, Habtewold D. Waktola, Dereje Kebebe, Sileshi Belew and Sultan Suleman in Environmental Health Insights

Supplemental Material

sj-docx-2-ehi-10.1177_11786302261454781 – Supplemental material for The Emerging Threat of Antibiotic Residues in the Aquatic Environments of East Africa: A Systematic Review

Supplemental material, sj-docx-2-ehi-10.1177_11786302261454781 for The Emerging Threat of Antibiotic Residues in the Aquatic Environments of East Africa: A Systematic Review by Duressa Dedefo, Gemmechu Hasen, Belachew Umeta, Desta Assefa, Yesuneh Tefera Mekasha, Simon Genet, Daniel Legese Achalu, Habtewold D. Waktola, Dereje Kebebe, Sileshi Belew and Sultan Suleman in Environmental Health Insights

Footnotes

ORCID iD

Daniel Legese Achalu

Author Contributions

DD: Conceptualization, Investigation, software, methodology, Validation, protocol preparation, Writing-review and editing. GH: Conceptualization, Investigation, software, methodology, Validation, Writing-review and editing. BU: Conceptualization, Investigation, software, methodology, Validation, Writing-review and editing. DA: Conceptualization, Investigation, software, methodology, Validation, Writing-review and editing. SG: Validation, writing-review and editing. DLA: Validation, writing-review and editing. YTM: Investigation, Methodology, Resources, Validation, protocol preparation, writing original draft, validation, writing-reviewing and editing. HDW: Conceptualization, Investigation, software, methodology, Validation, Writing-review and editing. SB: Conceptualization, Investigation, software, methodology, Validation, Writing-review and editing. SS: Conceptualization, Investigation, software, methodology, Validation, Supervision, Writing-review and editing.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

All data were within the manuscript, and additional information was attached as supplementary file.

Supplemental Material

Supplemental material for this article is available online.

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