Distribution and Levels of Contaminants of Emerging Concern in Surface Water of Imo River, Nigeria: A Non-Targeted Analysis.

Introduction

Many recent environmental studies have shown increasing presence of contaminants of emerging concern (CECs) in the environment. The aquatic environment is impacted significantly, raising global concerns due to potential adverse effects CECs could have on aquatic life, human health and the entire environment even at low concentrations (Sauve & Desrosiers, 2014; Yuange et al., 2024; Jianglu et al., 2024 ).

In a review of how one defines emerging contaminants preferably termed “contaminants of emerging concern”  and what can be included in that group of contaminants,  Sauve and  Desrosiers, (2014) gave a historical perspective  on the evolution of the issues surrounding emerging contaminants and how environmental scientists have tackled this issue. They noted that it began with global lead contamination from the Romans two millennia ago, moved on to arsenic-based and Dichlorodiphenyltrichloroethane (DDT) issues and more recently to pharmaceuticals, cyanotoxins, personal care products, nanoparticles, flame retardants, etc. Contaminants of emerging concern will remain a moving target as new chemical compounds are continuously produced and science continuously improves its understanding of current and past contaminants.

Contaminants of emerging concern (CECs) also referred to as emerging contaminants (ECs), or emerging pollutants (EPs), can be defined as newly identified synthetic or naturally occurring chemicals or biological agents that are detected in the environment and potentially hazardous or recently determined to be hazardous to humans and ecosystems. The risks associated with these contaminants are not fully understood, their toxicological significance is difficult to assess and generally accepted concentration limits for drinking water and discharge limits for wastewater effluent have not yet been established (Pal et al., 2014)  . They may include pharmaceuticals and personal care products (PPCPs), per- and poly-fluoroalkyl substances (PFAS), endocrine disruptors (EDs), emerging pathogens, cyanotoxins and other natural toxins, pesticides, industrial chemicals, micro/nano plastics, nanomaterials, antibiotic resistance genes (ARGs), and other exogenous substances that are found in the environment but are not yet well understood in terms of their impacts on humans and natural ecosystems (Fang et al., 2024; Enyoh et al., 2020; Ebele et al., 2017). The occurrence of these contaminants in the aquatic environment and especially in surface water is a serious public health concern because potable drinking water and water for other uses are primarily sourced from surface and ground waters in many countries (Abafe et al., 2023, Galindo-Miranda et al,. 2019)

Conventional water treatment processes were designed to tackle known inorganic and organic pollutants but with the increasing list of pollutants, treatment of water to potable standards have become increasingly difficult (Abafe et al., 2023).  The analysis of these pollutants in water for treatment and management purposes is usually achieved through targeted analysis approach, using established and validated liquid chromatography, coupled with gas chromatography mass spectrometry detection techniques (Pitarch et al., 2010).  However, these established techniques only cover a fraction of known pollutants, leaving many legacy and emerging compounds undetected and unstudied. Target analysis alone does not present the actual pollution status of the water systems (Abafe et al., 2023).

Non-targeted analysis (NTA) methods have unique value in that they can garner informative chemical measurements from samples of interest without the need for predefined chemical targets (McCord et al., 2022). The non–targeted analysis of environmental samples generally starts with the collection of samples to be analyzed, followed by analysis in which full scan mass spectrum (MS) data as well as tandem mass spectrum (MS/MS) fragmentation information is collected for identification purposes (Ng, 2021). After the data is acquired, one of the most important steps is the data pre-processing as it is required to make sense of the data and reduce not only the quantity, but also the complexity. This is done through a series of processes such as the detection of peaks, alignment of retention times, background subtraction using blanks. The final step in the identification of compounds of interest by NTA involves utilizing all the information obtained from the previous steps, in which the MS and MSn data are matched up with their respective molecular ion, isotopic pattern and fragments (Hollender et al., 2017; Ng, 2021). In a Study conducted by Wu et al., (2023), a total of 70 CECs was detected at least once at selected seventeen (17) sampling sites along the Yangtze River.  Twenty-four (24) CECs were detected at each site, and these were mostly pharmaceutical, personal care products and pesticides.

The Imo River located in south eastern Nigeria is a very important water resource that supports different human activities including, but not limited to fishing, agriculture, and domestic usage (Ogbonna et al., 2021). For the assessment of the occurrence and distribution of priority contaminants of emerging concern in Imo River, a non-targeted approach was employed to give insights into the actual CEC pollution level of the river.

Materials and Methods

Study Area

The Imo River, located in Southeastern Nigeria originates from the Imo State, and flows through Abia, Rivers and Akwa ibom states of Nigeria into the  Atlantic ocean (Ogbonna et al., 2021). According to the location/topographic map of the study region, the Imo River Basin is located between latitudes 4° 38'N and 6° 01'N and between longitudes 6° 53'E and 7° 32'E. It has an approximate area of 9100 km² (Uma, 1989). Three (3) sampling locations along the Imo river were selected for the study based on high human density with much anthropogenic activities. The three locations were, Ekenobizi (Imo State), Owerrinta (Abia State) and Oyigbo (Rivers State) (Figure 1). The coordinates for each of the sampled points were as follows; Ekenobizi upstream (Lat 5.558823⁰_, Long. 7.413593⁰)_, midstream (Lat 5.558852⁰, Long. 7.414024⁰), downstream (Lat 5.558812⁰, Long. 7.414057⁰), Owerrinta upstream (Lat 5. 30586, Long. 7.28721), midstream (Lat 5. 30599, Long. 7.28721), downstream (Lat 5.30776, Long. 7.28748) and Oyigbo upstream (Lat 4.89035, Long. 7.14274), midstream (Lat 4.88812, Long. 7.14351), downstream (Lat 4.88566, Long. 7.14792).

The activities  around the chosen locations as observed during reconnaissance surveys include dredging  and collection of sharp sand, waste disposal and fishing  common to the three locations. Other activities observed were farming activities, a major market that sold various household items and building materials , including various grinding mills at Ekenobizi area, animal sacrifices at the Owerrinta area and illegal petroleum exploration and a major abattoir at the Oyigbo area.

Figure 1: Overview of the Study Area and Sampled Locations

Fatty acids, such as Hexadecanoic acid and cis-Vaccenic acid, detected at significant concentrations, have been previously associated with anthropogenic  input from domestic, industrial and agricultural sources(Rudel et al., 2011, Meng et al., 2020). The detection of fluorinated fatty acid derivatives like Hexadecanoic acid, dodecafluoroheptyl ester raises concerns due to their association with perfluoroalkyl substances (PFAS). PFAS are globally recognized for their environmental persistence and bioaccumulation, posing risks to aquatic life and human health (Giesy & Kannan, 2002). Their detection in Imo River samples reflects patterns seen in polluted rivers worldwide, such as the Danube and Rhine (Ahrens et al., 2010).  High detection of fluorinated organics, including Triacontyl pentafluoropropionate and Octacosyl heptafluorobutyrate, reflects global concerns over PFAS-related compounds. PFAS contamination has been linked to adverse health outcomes in fish, such as liver damage and hormonal disruptions (De Silva et al., 2021). The findings corroborate similar studies in West African aquatic systems, where PFAS residues have been reported at concerning levels, necessitating urgent monitoring (Olutona et al., 2023).

The widespread presence of linear and branched alkanes (Pentadecane, Heptacosane, Eicosane), alongside PAH derivatives and biomarkers like Hopanes, suggests inputs from petroleum-related activities, urban runoff, or atmospheric deposition. Studies have shown that aliphatic hydrocarbons and hopanes are reliable indicators of oil pollution and crude oil contamination in aquatic environments (Wang et al., 2004). This aligns with the results especially from the Oyigbo axis (72.5% alkanes/alkenes) where illegal petroleum exploration was observed. Additionally, PAHs, known for their mutagenic and carcinogenic properties, pose significant ecological threats (Afolabi et al., 2024). Primary long-chain amines (Nonadecylamine, Dodecanamine) and nitrogenous amides suggest sources from agrochemical formulations, detergents, or industrial effluents. Long-chain amines can exhibit aquatic toxicity and contribute to bioaccumulation in fish (Poste et al., 2014). The presence of nitrogen-containing organic pollutants in aquatic systems is increasingly documented, with evidence linking such compounds to developmental toxicity in aquatic organisms.

The identification of halogenated compounds such as Bromoacetic acid esters, Methylene Chloride, and various brominated alkanes suggests both industrial discharge and degradation by-products from chlorination processes. Such compounds are persistent, bioaccumulative, and often exhibit toxicity to aquatic life (USEPA, 2018). Halogenated hydrocarbons are established indicators of anthropogenic pollution, especially in industrialized coastal regions (UNEP, 2019). Detection of nitrogenous heterocycles (Pyrimidine derivatives, Indole compounds) and aromatic amines points to pharmaceutical and agricultural runoff, consistent with recent research linking these classes to antimicrobial resistance hotspots in aquatic ecosystems (Kümmerer et al., 2018). The co-occurrence of persistent siloxanes, Fluorinated organics, PAHs, alkanes/alkenes  and Nitrogenous pollutants implies a complex mixture of contaminants, elevating risks of synergistic toxicity, bioaccumulation, and trophic transfer. Similar mixtures have been linked to endocrine disruption, reproductive impairment, and immune suppression in aquatic organisms (Ankley et al., 2005).

The Anova result which showed no significant difference among the CEC concentrations across the sampled locations suggests that the factors influencing the CEC contamination of the Imo River are similar and consistent enough across the sampled locations that they produce no measurable difference in the CEC levels. This is consistent with the similar anthropogenic presence and activities at the various locations.

Conclusion

The  non-target analysis (NTA) of surface water from the Imo River at Ekenobizi, Owerrinta and Oyigbo using GCMS was able to establish the presence of various contaminant compounds of emerging concerns. A total of 85 unique CECs was detected. The detected compounds were of diverse parent/functional groups with diverse chemical characteristics.

The detection and concentration patterns of Contaminants of Emerging Concern (CECs) in the Imo River surface water reveal critical trends of environmental contamination and potential ecological risks, consistent with global studies. The findings underscore significant contamination of the Imo River system with a broad spectrum of emerging organic pollutants, including siloxanes, fatty acids, amines/amides, alkanes/alkenes and fluorinated compounds. Findings resonate with global research on the persistence, mobility, and ecological risks of these contaminants.

1. Targeted analysis of detected CECs for the purpose of setting permissible health limits and standards for treatment and management purposes.

2. Implementation of stricter monitoring and control of industrial effluents, especially from manufacturing, petroleum, and personal care product industries, which are known sources of siloxanes, amines, and fatty acids.

3.Promotion of sustainable farming practices to reduce the discharge of fatty acids and nutrient-rich compounds into the river, as supported by global mitigation strategies.

4.Establishment of a long-term, monitoring framework targeting CECs in surface water, following international guidelines for surface water quality preservation.

5.There is need for public health awareness in form of consumption advisories for surface waters and to discourage household waste disposal into the river for communities around the Imo River.

6.Replacement of high-risk compounds, particularly persistent siloxanes and fluorinated esters, with biodegradable alternatives, aligning with global green chemistry initiatives.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Credit Authorship Contribution Statement

Humphrey–Ebenezer, J. N: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Data curation, Visualization, Project administration, Writing - original draft. Nwakanma, C. & Nzegbule, E.: Supervision, Methodology, Validation, Formal analysis, Data curation, Visualization, Review & Editing.