Accumulation of ibuprofen in endemic amphipods of Lake Baikal

Accumulation of ibuprofen in endemic amphipods of Lake Baikal | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Accumulation of ibuprofen in endemic amphipods of Lake Baikal View ORCID Profile Tamara Y. Telnova , View ORCID Profile Maria M. Morgunova , View ORCID Profile Sophie S. Shashkina , View ORCID Profile Maria E. Dmitrieva , View ORCID Profile Victoria N. Shelkovnikova , View ORCID Profile Olga E. Lipatova , View ORCID Profile Ekaterina V. Malygina , View ORCID Profile Natalia A. Imidoeva , View ORCID Profile Alexander Y. Belyshenko , View ORCID Profile Tatyana N. Vavilina , View ORCID Profile Arkadii N. Matveev , View ORCID Profile Evgenia A. Misharina , View ORCID Profile Denis V. Axenov-Gribanov doi: https://doi.org/10.1101/2025.09.04.673924 Tamara Y. Telnova 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Tamara Y. Telnova Maria M. Morgunova 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Maria M. Morgunova Sophie S. Shashkina 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Sophie S. Shashkina Maria E. Dmitrieva 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Maria E. Dmitrieva Victoria N. Shelkovnikova 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Victoria N. Shelkovnikova Olga E. Lipatova 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Olga E. Lipatova Ekaterina V. Malygina 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Ekaterina V. Malygina Natalia A. Imidoeva 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Natalia A. Imidoeva Alexander Y. Belyshenko 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Alexander Y. Belyshenko Tatyana N. Vavilina 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Tatyana N. Vavilina Arkadii N. Matveev 2 UNESCO Chair on Water Resources, Irkutsk State University , Irkutsk, Russia 3 Institute of biological sciences, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Arkadii N. Matveev Evgenia A. Misharina 3 Institute of biological sciences, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Evgenia A. Misharina Denis V. Axenov-Gribanov 1 Bioorganics Research and Educational Center, Irkutsk State University , Irkutsk, Russia 3 Institute of biological sciences, Irkutsk State University , Irkutsk, Russia Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Denis V. Axenov-Gribanov For correspondence: denis.axengri{at}gmail.com Abstract Full Text Info/History Metrics Preview PDF Abstract Pharmaceutical pollutants, including ibuprofen, are now ubiquitously detected in global aquatic ecosystems, exerting significant negative ecological impacts. Lake Baikal organisms have been documented to accumulate ibuprofen and related contaminants. This study quantified ibuprofen concentrations within Lake Baikal’s endemic amphipod fauna using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). We analyzed specimens representing key ecological groups across the genera Eulimnogammarus, Brandtia, Ommatogammarus , and Pallasea . Ibuprofen concentrations ranged from 4.19 ng/g to 1151.32 ng/g (wet weight), confirming consistent contamination in both littoral and deep-water endemic amphipod populations. Crucially, our data provide the first evidence suggesting amphipods, or their associated symbiotic microbiota, may metabolize ibuprofen. Interspecific accumulation patterns were identified, with Eulimnogammarus sp. and Brandtia sp. exhibiting distinct profiles. Furthermore, accumulation was significantly higher during spring compared to autumn samples. A negative correlation emerged between ibuprofen concentration and amphipod body mass within species. Several populations contained non-detectable levels. These findings demonstrate that endemic amphipods within Lake Baikal’s natural environment are exposed to and bioaccumulate the pharmaceutical pollutant ibuprofen, exhibiting species-specific, seasonal, and allometric variation in uptake. INTRODUCTION Pharmaceuticals are indispensable in modern healthcare and daily life, safeguarding public health while enhancing quality and longevity. Non-steroidal anti-inflammatory drugs (NSAIDs) constitute a major therapeutic class, extensively employed in human and veterinary medicine for their analgesic, antipyretic, and anti-inflammatory properties ( Parolini, 2020 ). Global accessibility and prevalence drive escalating NSAID demand and production. However, regulatory oversight remains limited, with most NSAIDs available over-the-counter ( Jan-Roblero & Cruz-Maya, 2023 ). An estimated 30 million individuals use NSAIDs daily, exceeding 300 million users annually worldwide. This high consumption poses significant environmental challenges ( Nieto et al., 2017 ; Jurado et al., 2021 ) due to incomplete drug metabolism in organisms, inadequate disposal practices and insufficient removal by wastewater treatment facilities. Following ingestion, a substantial fraction of NSAIDs is excreted unmetabolized or as bioactive compounds ( Marchlewicz et al., 2015 ), ultimately entering aquatic ecosystems. The resultant influx of pharmaceutical pollutants exerts detrimental effects on freshwater biota. Monitoring studies consistently detect NSAIDs— including acetylsalicylic acid, paracetamol (acetaminophen), diclofenac, ketoprofen, and naproxen— in freshwater systems globally ( Tyumina et al., 2020 ), underscoring their pervasive environmental presence. Notably, ibuprofen stands out among NSAIDs due to its extensive clinical use and inclusion on the World Health Organization’s List of Essential Medicines (Chopra & Kumar, 2020). However, its high global consumption—with annual production exceeding 300,000 tonnes ( Marchlewicz et al., 2015 )—presents a significant environmental risk. Ibuprofen exhibits limited aqueous solubility and undergoes incomplete metabolism in humans. Following excretion, it enters the environment either unmetabolized or as biotransformation products, primarily hydroxyibuprofen, carboxyibuprofen, carboxyhydratropic acid (Chopra & Kumar, 2020), and 4-isobutylcatechol ( Larsen, 2019 ). These metabolites often undergo further hydrolysis and are frequently more toxic to aquatic organisms than the parent compound (Chopra & Kumar, 2020). Global monitoring studies confirm ibuprofen’s pervasive presence in aquatic systems. Reported concentrations in surface waters range from 0.98 to 1.417 µg/L across diverse regions including Canada, France, China, Greece, Korea, Taiwan, and Uganda ( Kim et al., 2009 ; Vulliet, 2011 ; Almeida et al., 2013; Luo et al., 2014 ; Nantaba et al., 2020 ). Conversely, groundwater studies in Europe report lower but still detectable levels, ranging from 3 to 395 ng/L ( Luo et al., 2014 ), underscoring its environmental persistence. Furthermore, ibuprofen and its metabolites exert demonstrable toxicity on aquatic organisms ( Das et al., 2019 ). Field studies confirm bioaccumulation across taxa: Hydropsyche spp. caddisflies in Spain’s Segre River contained 184 ng/g ibuprofen ( Huerta et al., 2015 ), while Gammarus fossarum amphipods downstream of a wastewater treatment plant in southern France showed concentrations of 60.6–105.4 ng/g ( Berlioz-Barbier et al., 2014 ). In urbanized Chinese rivers, ibuprofen was detected in phytoplankton (14.5–35.8 ng/g), zooplankton (20.9–48.9 ng/g), and benthic invertebrates (freshwater shrimp, mussels, snails: 4.8–11.6 ng/g) ( Yang et al., 2020 ). Laboratory studies indicate adverse effects occur at concentrations typically orders of magnitude higher than environmental levels (10–100 mg/L) ( Pajić et al., 2023 ). Documented toxicity spans diverse aquatic taxa, including echinoderms ( Asterias rubens, Psammechinus miliaris ), polychaetes ( Arenicola marina ), microalgae ( Navicula sp., Chlorella vulgaris, Acutodesmus obliquus, Chlamydomonas reinhardtii, Nannochloropsis limnetica ), and crustaceans ( Daphnia magna ) ( Grzesiuk, 2016 ; Geiger, 2016 ; Du et al., 2016 ; Zanuri, 2017 ; Ding et al., 2019 ). These findings underscore that ibuprofen contamination poses a potential yet understudied threat to ancient aquatic ecosystems. Lake Baikal – a tectonic-formed UNESCO World Heritage site in southeastern Siberia – represents a critical case study as Earth’s deepest lake ( Moore et al., 2009 , 2019 ; Rusinek et al., 2012 ) and one of its most ancient, with recent geological evidence indicating an age exceeding 60 million years ( Matz & Efimova, 2017 ). This evolutionary cradle harbors >2,600 animal species exhibiting exceptional endemism ( Timoshkin et al., 2016 ), heightening vulnerability to anthropogenic pollutants like ibuprofen. As in all aquatic ecosystems, pollutants in Lake Baikal undergo trophic transfer via nekton, plankton, and benthos (Rusinek et al., 2015). Among endemic benthic taxa, amphipods (Amphipoda, Crustacea) represent a hyperdiverse and ubiquitous group occupying all depth zones and substrate types ( Takhteev, 2019 ). This ecological dominance positions them as sentinel organisms for early pollutant exposure. Critically, recent research confirms Baikal amphipods bioaccumulate multiple pharmaceuticals—including acetylsalicylic acid, paracetamol, tetracycline antibiotics, and notably ibuprofen ( Telnova et al., 2024 ). The persistent detection of ibuprofen, a compound with established ecotoxicity, signals direct risks to endemic species and broader lake ecosystem integrity. To address key knowledge gaps, this study quantifies species- and population-specific ibuprofen concentrations in endemic Baikal amphipods and evaluates seasonal accumulation dynamics. MATERIALS AND METHODS The current study focused on adult amphipods spanning key ecological niches within Lake Baikal. Specimens included littoral species ( Eulimnogammarus cyaneus (Dybowsky, 1874), E. verrucosus (Gerstfeldt, 1858), and unidentified Eulimnogammarus specimens), free-living sublittoral species ( Brandtia sp. (Bate, 1862)), sublittoral benthic species ( Pallasea sp. (Bate, 1862)), and deep-water species Ommatogammarus flavus (Dybowsky, 1874). Detailed ecological and physiological characterization of these taxa was well described in earlier studies ( Axenov-Gribanov et al., 2016 ; Shirokova et al., 2024; Drozdova et al., 2025 ). Amphipods related to species E. verrucosus were collected from littoral zones at: Kultuk, Listvyanka, Bolshoye Goloustnoye, Ust-Barguzin, and Buguldeika settlements (South and Middle Baikal) during spring 2023. Additional specimens were obtained from the Angara River in Irkutsk city. The place of sampling in Angara was located upstream of municipal wastewater treatment facilities. Listvyanka populations of E. verrucosus were sampled seasonally (spring and autumn 2023). Specimens of E. cyaneus were obtained from littoral zone of Angara River during spring 2023. Amphipods of Brandtia sp. were collected concurrently at two sites: the Angara River and Listvyanka settlement. O. flavus was collected from the profundal zone (70 m depth) near Buguldeika settlement using hydrobiological traps (spring 2023). All specimens were collected with hydrobiological nets except where noted. All specimens were immediately transferred to 2 mL plastic Eppendorf tubes, flash-frozen in liquid nitrogen, and stored at −196°C. Sampling locations are shown in Figure 1 . Lake Baikal experiences intense recreational pressure as a major tourism hub, with all sampling sites situated in highly frequented destinations ( Aleksandrova et al., 2021 ). This anthropogenic context heightens contamination risks from pharmaceutical residues in nearshore ecosystems. Download figure Open in new tab Fig. 1. Map of amphipod sampling sites, Lake Baikal The study included two stages, and involved qualitative and quantitative assessments of ibuprofen content in amphipods. Each amphipod was weighed individually on an analytical balance (Sartorius CE224-C, St. Petersburg, Russia) and homogenized three times in a vibratory ball mill (BABRx1, Mycotech, Irkutsk, Russia) with acetonitrile ( Telnova et al., 2024 ). After each grinding cycle, samples were briefly centrifuged at 1,000 rpm for 1 min (Armed LC-04B, St. Petersburg, Russia) to separate supernatant and debris. Supernatant was transferred into new 2-mL Eppendorf tubes, and debris was re-extracted. After complete extraction, samples were brought to a final volume of 4 mL with acetonitrile. The tubes were centrifuged (Armed LC-04B, St. Petersburg, Russia) for 10 minutes at 3,000 rpm. 2-mL aliquot of supernatant was transferred into glass vials and concentrated in a vacuum oven (Stegler VAC-52 FCD-3000, Shanghai, China). The dried residues were reconstituted in 1 mL of 40:60 (v/v) acetonitrile/milli-Q water. Extracts underwent ultrasonication for 10 minutes and were transferred to microtubes. 50 µL of 10% trichloroacetic acid solution was added to each sample. Microtubes were vortex-mixed for 1 minute and centrifuged at 16,000 rpm during 10 min (Microspin-12, Biosan Riga, Latvia) ( Gonzalez-Rey and Bebianno, 2012 ). Prior to analysis, samples were filtered through 13-mm PVDF syringe membranes (0.45-µm pore size). A 200-µL aliquot of filtrate was transferred to HPLC vials for analysis. During the study, three types of samples were measured: amphipod extracts (a), ibuprofen analytical standard solution (Certified Reference Material 11559-2020, NCAS, Moscow, Russia) (b), and amphipod extracts spiked with ibuprofen standard (c). The analytical standard solution was used to optimize ionization parameters and evaluate chromatographic system performance ( Eraga et al., 2015 ). Subsequently, amphipod extracts were analyzed both unmodified and following standard addition. The concentration of the ibuprofen analytical standard working solution was 72 ng/mL. Spiked samples consisted of 600 µL amphipod extract and 100 µL ibuprofen analytical standard solution (final volume: 700 µL) ( Bashyal, 2018 ; Dowling et al., 2020). A linear calibration curve was generated for ibuprofen concentrations ranging from 0,025 ng/mL to 50 ng/mL. Screening for ibuprofen in Baikal endemic amphipods was performed using an Agilent Infinity II (2019) LC-MS/MS system equipped with an Agilent 6470B triple quadrupole mass spectrometer. Chromatographic separation used an Agilent Poroshell C18 column (2.1 × 50 mm) maintained at 30°C. Table 1 presents the program for HPLC separation of samples containing ibuprofen. Mass spectrometer setup program: ion source gas temperature: 300 °C; ion source gas flow: 5 L/min; nebuliser: 45 psi; drying gas temperature: 250 °C; drying gas flow: 11 L/min; capillary voltage: 3500 V; sample volume: 1 µL. Ibuprofen detection used MRM transition 205.1 → 161.1 (GOST 32881-2014, Moscow, Russia). View this table: View inline View popup Download powerpoint Table 1. HPLC gradient program for ibuprofen separation The study involved analysis of 218 specimens of Baikal amphipods, including E. verrucosus (n=180), O. flavus (n=20), E. cyaneus (n=3), and unidentified amphipods of the genera Eulimnogammarus (n=8), Brandtia sp. (n=6), and Pallasea sp. (n=1). Samples of E. verrucosus and Brandtia sp. comprised single individuals. Analyses of O. flavus and E. cyaneus utilized pooled samples containing two individuals each. The statistical processing was performed in Past software (V4.03) using the Kruskal–Wallis H test (one-way ANOVA on ranks as a non-parametric method) for the analysis of qualitative data. The Bonferroni sequential significance model was used. One-way ANOVA, t-test and F-test were used to analyze quantitative data. The effects of factors “year of sampling” and “wet weight of amphipods” were reported based on two-way ANOVA. To determine which group means were significantly different from each other, Tukey’s post-hoc tests were performed. Differences between the mean values of the parameters were considered significant at p ≤ 0.05. RESULTS Qualitative assessment of the ibuprofen presence in Baikal endemic amphipod Qualitative assessment of ibuprofen presence was carried out in amphipods of the species Eulimnogammarus verrucosus collected in autumn 2023 and Ommatogammarus flavus collected in spring 2023. The qualitative analysis demonstrated that ibuprofen was detected in E. verrucosus collected in the Angara River, Listvyanka settl., and Buguldeyka settl. The detection frequency of ibuprofen contamination in amphipods ranged from 12% to 27%. Ibuprofen was not detected in amphipods collected in Bolshoye Goloustnoye, Kultuk, and Ust-Barguzin settlements ( Fig. 2 ). Download figure Open in new tab Fig. 2. Qualitative assessment of ibuprofen in distinct populations of E. verrucosus – E. verrucosus contaminated with ibuprofen; – clean samples The chromatogram of the ibuprofen analytical standard ( Fig. 3a ), chromatogram of ibuprofen detected in E. verrucosus ( Fig. 3b ), and chromatogram of amphipod extract spiked with ibuprofen standard ( Fig. 3c ) demonstrate identical retention times and mass spectra, confirming ibuprofen presence in endemic amphipods. Download figure Open in new tab Fig. 3. Representative chromatograms: (A) Ibuprofen analytical standard; (B) Ibuprofen detected in E. verrucosus extract; (C) E. verrucosus extract spiked with ibuprofen standard Ibuprofen was detected in the deep-water amphipod O. flavus collected at 70 m depth near Buguldeika settl. One of 20 analyzed specimens tested positive for ibuprofen. Representative chromatograms are shown in Figure 4 . Also, qualitative assessment confirmed ibuprofen presence in E. cyaneus and Pallasea sp. However, insufficient biomaterial precluded quantification of contamination levels or internal ibuprofen concentrations. Download figure Open in new tab Fig. 4. Representative chromatograms of ibuprofen detection: (A) Analytical standard; (B) O. flavus extract with detected ibuprofen Quantitative assessment of ibuprofen content in Baikal endemic amphipod Quantitative assessment of ibuprofen in E. verrucosus from Listvyanka settl. revealed significantly higher accumulation during spring 2023 compared to autumn 2023 (p = 0.001). Spring amphipods accumulated twice the ibuprofen levels measured in their autumn counterparts ( Fig. 5 ). This seasonal difference indicates dynamic bioaccumulation patterns in Baikal’s endemic amphipods. Download figure Open in new tab Fig. 5. Concentration of ibuprofen (in ng/g) in amphipods of species E. verrucosus collected in two seasons in Listvyanka settl. in 2023 In E. verrucosus collected during spring, ibuprofen concentrations ranged from 14.92 to 166.38 ng/g, while wet weights ranged from 74 to 776 mg. During autumn, concentrations ranged from 4.19 to 29.65 ng/g, with wet weights spanning 213 to 431 mg. Amphipods of the genera Eulimnogammarus and Brandtia collected from the Angara River in spring 2023 were subsequently analyzed. Quantitative assessment revealed significant interspecific differences in ibuprofen accumulation: Brandtia specimens accumulated fourfold higher concentrations than Eulimnogammarus (p = 0.001; Fig. 6 ). In amphipods of the genus Eulimnogammarus , ibuprofen concentrations ranged from 16.84 to 46.50 ng/g, with individual wet weights spanning 285 mg to 440 mg. For amphipods of the genus Brandtia , wet weights ranged from 28 mg to 68 mg, while ibuprofen concentrations ranged from 174.9 to 439.69 ng/g. Download figure Open in new tab Fig. 6. Concentration of ibuprofen (in ng/g) in amphipods of genera Eulimnogammarus and Brandtia , collected in the Angara River The maximum ibuprofen concentration was detected in E. verrucosus collected during autumn near Buguldeika settl. ( Fig. 7 ). For specimens with wet weights ranging from 105 mg to 307 mg, ibuprofen levels ranged from 18.33 to 1151.32 ng/g. In the studied individual of Pallasea sp. (wet weight: 0.130 g), ibuprofen was detected at 84.86 ng/g, while the concentration in deep-water O. flavus was 5.15 ng/g. Download figure Open in new tab Fig. 7. Concentration of ibuprofen (in ng/g) in amphipods collected in two seasons in 2023 Note: letter designations of amphipod groups denote statistically significant differences Furthermore, a dependence of ibuprofen concentration on organism wet weight was observed in E. verrucosus collected during autumn near Listvyanka settl. ( Fig. 8 ). In amphipods with wet weights from 0.21 to 0.29 g, the maximum ibuprofen concentration reached 29.65 ng/g, while specimens weighing 0.43 g contained ibuprofen at 4.19 ng/g. This weight-concentration relationship was also evident in Brandtia spp. from the Angara River ( Fig. 9 ), where amphipods weighing 0.028-0.036 g showed concentrations of 385.03-431.63 ng/g, whereas a 0.068 g specimen accumulated ibuprofen at 174.90 ng/g. Download figure Open in new tab Fig. 8. The correlation between the concentration of accumulated ibuprofen and wet weight of amphipod E. verrucosus (in ng/g). Sampling site: Listvyanka settl. (autumn 2023) Download figure Open in new tab Fig. 9. The correlation between the concentration of accumulated ibuprofen and wet weight of amphipod Brandtia (in ng/g). Sampling site: Angara River (spring 2023) Additionally, a compound structurally similar to ibuprofen was detected in several E. verrucosus specimens. While ibuprofen shows MRM transition 205.1 → 161.1, this compound exhibited a retention time shift of +0.2 minutes ( Fig. 10C ) with identical mass transitions. We hypothesize that this substance corresponds to the ibuprofen metabolite, since both substances have a similar fragmentation pattern and a similar retention time. An ibuprofen derivative was detected in E. verrucosus collected from the Angara River, Listvyanka, Bolshoye Goloustnoye and Buguldeika settlements ( Fig. 11 ). The detection frequency of this derivative ranged from 10% to 50%. It was not detected in E. verrucosus from Kultuk and Ust-Barguzin settlements, nor in the deep-water amphipod O. flavus . Download figure Open in new tab Fig. 10. Representative chromatograms: (A) Ibuprofen analytical standard; (B) Suspected ibuprofen metabolite in E. verrucosus extract; (C) E. verrucosus extract spiked with ibuprofen standard Download figure Open in new tab Fig. 11. Evaluation of the presence of ibuprofen derivative in different populations of amphipod species E. verrucosus – E. verrucosus contaminated with ibuprofen derivative; – clean samples DISCUSSION Pharmaceutical bioaccumulation in Lake Baikal’s ecosystem represents an urgent ecological concern. Initial studies confirmed trace drug residues in endemic amphipods, including acetylsalicylic acid, paracetamol, azithromycin, tetracyclines, amikacin, dimetridazole, metronidazole, and spiramycin. Earlier ibuprofen detection was reported by our studies, published by Telnova et al. (2024) , who analyzed E. verrucosus from a Bolshoe Goloustnoe settl. in August 2020 and 2022. This monitoring revealed significant temporal variation: ibuprofen was detected in 70% of specimens in 2020 versus 27% in 2022. Our 2023 analysis revealed no direct ibuprofen contamination. Here we detected ibuprofen transformation products in 34% of E. verrucosus specimens. While ibuprofen metabolite screening was not conducted in 2020-2022, the declining parent compound concentration may reflect reduced post-pandemic pharmaceutical loading. These findings demonstrate that Baikal amphipods experience intermittent, but recurrent, pharmaceutical exposure with shifting contaminant profiles. Quantitative analysis confirmed a significant inverse relationship between amphipod wet weight and accumulated ibuprofen concentrations. Maximum ibuprofen levels occurred in E. verrucosus from Buguldeika settl. Interspecific comparisons of Eulimnogammarus sp. and Brandtia sp. in the Angara River revealed differential bioaccumulation capacities. These patterns likely reflect morphological adaptations, particularly differences in integument permeability and exoskeleton composition affecting chemical uptake. Supporting this mechanism, Jakob et al. (2017) demonstrated reduced cadmium accumulation in larger E. verrucosus versus smaller E. cyaneus – attributable to allometric scaling of surface-area-to-volume ratios. Such size- and species-dependent accumulation principles appear conserved across pollutant classes, extending to pharmaceutical contaminants in Baikal amphipods. Previous studies (Meyer et al., 2022) detected pharmaceuticals in Lake Baikal water including paracetamol (acetaminophen), paraxanthine, caffeine, cotinine, cimetidine, diphenhydramine, phenazone and sulphachloropyridazine at concentrations of 1–64 ng/L (equivalent to 0.001–0.064 ng/g). Contrastingly, our 2023 data reveal substantial bioaccumulation in endemic amphipods, with ibuprofen concentrations ranging from 4.19 to 1151.32 ng/g – representing bioaccumulation factors (BAFs) of 65,500 to 1,151,320 relative to environmental concentrations ( Chen et al., 2023 ). Conservative estimates indicate amphipods concentrate ibuprofen at 4,000–17,000× environmental levels when compared to typical non-zero contaminant measurements (≥1 ng/L). This demonstrates exceptional biomagnification capacity within Baikal’s trophic web. We propose that littoral E. verrucosus metabolizes ibuprofen, evidenced by a consistent 0.2-minute chromatographic retention time shift with identical mass fragmentation (MRM 205.1→161.1), indicating structural analogs. This derivative likely forms via amphipod enzymatic or symbiotic biotransformation. Notably, the metabolite was absent in E. verrucosus from Kultuk and Ust-Barguzin settlements. The accumulation of active pharmaceutical ingredients like ibuprofen in Lake Baikal’s endemic amphipods originates from anthropogenic sources, entering the ecosystem via sewage discharge and groundwater infiltration—either as parent compounds or bioactive metabolites ( Timoshkin et al., 2016 ). As a synthetic xenobiotic, ibuprofen lacks natural emission pathways. This contamination is exacerbated by Baikal’s status as a major recreational hub, where tourism and local usage drive pharmaceutical loading into nearshore environments. This study identifies Listvyanka settlement as a principal ibuprofen contamination hotspot, where E. verrucosus amphipods exhibit dual exposure responses: bioaccumulation of parent compounds and metabolic transformation into derivatives. Anthropogenic loading likely stems from intensive tourism and inadequate wastewater treatment, compounded by seasonal dynamics. Quantitative analysis confirms significantly higher concentrations in spring-collected specimens versus autumn, potentially reflecting elevated pharmaceutical consumption during winter illness peaks. Hydrographic processes critically govern ibuprofen distribution in Lake Baikal, where the counter-clockwise surface current (0.5–1.8 m/s) transports contaminants southward along the western shore from high-tourism zones (Maloe More and Olkhon Island) toward downstream settlements. This advective flow establishes a contamination gradient: Buguldeika—closest to northern sources (50 km from Olkhon) and directly within the current – exhibited peak concentrations (1151 ng/g); Listvyanka (mid-transit, 85 km downstream) showed moderate levels (166 ng/g); while Kultuk, positioned beyond the Khamar-Daban coastal deflection zone and farthest from sources (120 km), showed no contamination. This spatial pattern correlates with Olkhon Island’s 300% tourism increase since 2015 ( Aleksandrova et al., 2021 ), confirming current-mediated dispersal as the primary distribution mechanism for pharmaceutical pollutants in Baikal’s pelagic ecosystem. As previously noted, pharmaceutical pollution in Lake Baikal’s waters is significantly driven by the absence of treatment facilities near populated areas and tourist hubs, improper disposal of expired medications, and seasonal disease outbreaks in humans. Critically, no data currently exist on the effects of ibuprofen—or other pharmaceuticals—on amphipods or any endemic Baikal species. Nevertheless, synergistic interactions between pharmaceutical contamination and compounding stressors—including climate change, escalating cyanobacterial proliferation risks, the decline of Baikal sponges, and tourism pressures on sites like Olkhon Island—threaten to accelerate biodiversity loss and facilitate invasive species establishment in the near future ( Timoshkin et al., 2016 ; Moore et al., 2009 , 2019 ). Ongoing monitoring efforts have accumulated a substantial body of data, underscoring both the escalating environmental threat and the critical need for sustained surveillance and proactive conservation measures. CONCLUSIONS This study establishes that endemic littoral and deep-water amphipods in Lake Baikal exhibit sustained ibuprofen contamination. We demonstrate for the first time that amphipods—potentially aided by symbiotic microorganisms—metabolize ibuprofen. Furthermore, Baikal amphipods bioaccumulate this pharmaceutical compound, with significantly higher concentrations observed in spring compared to autumn. Bioaccumulation capacity correlates positively with amphipod body mass, while several populations remain uncontaminated despite proximity to pollution sources. Collectively, these findings confirm that wild populations of endemic Baikal amphipods are chronically exposed to ibuprofen within their natural habitat. Funding The study was carried out with the financial support of the project of the Ministry of Higher Education and Science of the Russian Federation (FZZE 2024-0011, FZZE 2024-0003) Competing Interests The authors have no relevant financial or nonfinancial interests to disclose Ethical Approval This is not applicable Consent to Participate This is not applicable Consent to Publish This is not applicable Funder Information Declared The Ministry of Higher Education and Science of the Russian Federation , FZZE 2024-0011 The Ministry of Higher Education and Science of the Russian Federation , FZZE 2024-0003 REFERENCES ↵ Aleksandrova A. Y. , Bobylev S. N. , Solovyeva S. V. , Khovavko I. Y. 2021 . Overtourism at Baikal: problems and ways of addressing them . 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