# Revealing the past: Sedimentary archives as historical records of ionizable organic contaminant trends

Thomas Thiebault

EPHE, PSL University, UMR 7619, METIS, Sorbonne University, CNRS, 4 place Jussieu, F-75005, Paris, France

## ARTICLE INFO

### Keywords:

- Sediments
- Wastewater
- Pharmaceuticals
- PFAS
- Pesticides
- Regulations
- Geochronology

## ABSTRACT

Sedimentary archives offer a valuable means to reconstruct historical trends of ionizable organic contaminants (IOCs) in aquatic environments. While research has traditionally emphasized hydrophobic pollutants, interest in IOCs, such as pharmaceuticals, pesticides, PFAS, and surfactants, has grown due to their pseudo-persistence and widespread use. This review explores how sediment records can reveal past contamination and regulatory impacts, despite challenges like complex sorption mechanisms, pH variability, and dating uncertainties. Although linking sediment concentrations to historical water quality remains challenging, temporal trends often align with market approvals, regulations, and treatment upgrades. Advances in non-target screening also enable retrospective identification of previously undetected compounds. Despite remaining uncertainties, sediment archives complement water monitoring and enhance understanding of long-term environmental change. Continued interdisciplinary research is essential to improve quantification methods and inform future pollution management and policy decisions.

## 1. Introduction

The particulate fraction has long been recognized as a carrier of organic contaminants [1] through various processes, in particular, adsorption [2]. Most of studies were historically conducted to assess the particulate occurrences of rather hydrophobic contaminants or to assess the relative distribution between water and particulate fraction, e.g. through $K_d$ assessment [3]. Beyond the work on the water-sediment interface [4] and partition coefficient [5] another type of research aims to analyze the historical distribution of contaminants within sedimentary archives, sampled in sediment accumulation zones [6]. These provide selective access to samples which, once dated, are classically considered representative of the dissolved contamination at the time of their deposition. These study objects enable research across highly variable timescales, ranging from several hundreds of thousands of years for oceanic cores to the past century for fluvial cores, with equally variable temporal resolutions [7].

Sedimentary archives are therefore valuable tools for retrospectively evaluating the trajectory of the chemical quality of the environment during periods when analytical chemistry was not as precise as it is today or when monitoring of the chemical quality of environmental compartments were not conducted [8], particularly since the

development of organic contaminant analyses in the 1980s. Quantitative assessments based on these archives remains largely challenging, due to several uncertainties (i) is the sedimentary content representative of the historical contamination, and (ii) what kind of normalization has to be performed in order to close the loop between dissolved and sedimentary concentration trends. However answer these two question appears mandatory in order to testify the interest of such historical contamination evaluation in order to document the impact of regulatory changes or contamination source management.

These questions have been mostly answered concerning hydrophobic contaminants, such as persistent organic pollutants and trace metals, as due to their physical-chemical properties, the particulate transport and fate is majoritarian in term of flux [9]. Analyzing such compounds in sediments therefore appeared as logical, and several normalization parameters, as total organic carbon have already been highlighted. However, most of these contaminations appeared to be quite ancient, or historical, and the strong development of chemical industry after WWII has considerably increased the total use and diversity of molecules on the market, with a strongly enlarged properties spectra, during the so-called "Great Acceleration" [10].

The recent analytical development allows to monitor numerous molecules, since 30 years, even if their market launch was largely older.
It therefore exists a significant discrepancy between a potentially existing contamination and our state of knowledge of its existence in the last century. It is especially true for IOCs, which are classically more polar and hydrophilic than historical contaminants as PCBs and PAHs, and for which sedimentary occurrences did not appear obvious. These compounds include a diverse range of substances, such as pharmaceuticals, pesticides (if we exclude organic chlorine and organo phosphate pesticides), and industrial chemicals as PFAS and surfactants. Their ionizable nature affects their solubility, bioavailability, transport mechanisms, and environmental persistence, making them a critical focus for understanding pollutant dynamics [11]. In particular their affinity with solids is more complex than for non-polar molecules, which other mechanisms as ion exchange and strong impact of moderate pH changes especially for weak bases and acids [12,13]. Their more, but not systematic in case of amphiphilic properties, hydrophilic properties also potentially increase the impact of non-organic phases, such as clays, in their sorption [14,15].

When dealing with the historical distribution of IOCs, beyond the observation of occurrence variability, the main question is the relevance of performing a quantitative link between the sedimentary occurrence and the historical chemical quality beyond external factors, e.g. by assuming the lack of significant degradation of mobility in the sedimentary column. A proper evaluation of IOCs in sedimentary archives also has significant implications for environmental management and policy. Historical data on the occurrence and distribution of these compounds can inform risk assessments, guide remediation efforts, and shape regulatory frameworks. For instance, understanding the legacy of persistent IOCs can help prioritize contaminated sites for remediation or identify regions at risk of future pollution. Similarly, historical trends in compound usage and environmental impact can provide valuable feedback for regulatory policies, such as restrictions on specific chemical classes or the development of safer alternatives.

This work therefore aims to review studies dealing with historical distribution of IOCs (pharmaceuticals, pesticides, PFAS and surfactants) in sedimentary archives, with a focus on dated archives in order to (i) evaluate the historical chemical quality evolution on a global scale, (ii) evaluate specific local patterns related to waste management and regulatory decisions, (iii) assess the potential of sedimentary archives to quantitatively assess historical use, and (iv) assess the potential of ionizable chemicals occurrence in sediments to support political decisions.

## 2. Methods

### 2.1. Literature searching and screening

Data for this review were collected from original research articles sourced from databases such as Web of Science and Google Scholar. In line with the objectives of this article, which aims to review studies advancing our understanding of IOCs in dated sedimentary archives, the keywords/phrases used in the search included "sedimentary archives" combined with contaminant typologies such as "surfactants," "pharmaceuticals," "pesticides," and/or "PFAS." Articles were then screened based on their provision of useful parameters, such as the adequacy of analytical information and their relevance to the discussion. For instance, studies focused on non-ionizable contaminants, such as organochlorine pesticides and non-ionic surfactants, were excluded. Additionally, papers addressing the water/sediment interface were excluded from the core of this review, although some of them are cited hereafter due to their insights into the sedimentary occurrence of contaminants and the exploration of contaminant affinity with sediments. Manuscripts dealing with IOC occurrences within non dated archives were also excluded of the heart of this review (n = 7). Ultimately, 36 relevant publications were included in this review, without applying any geographical or temporal sorting criteria.

### 2.2. Study evaluation and contaminant of interest

After the selection, raw data were extracted from publications provided that the following criteria were met: (i) IOC belonging to pharmaceuticals, surfactants, pesticides or PFAS were quantified in sediments, (ii) sedimentary core was properly dated and the used isotopes, (iii) basic geochemical analyses of the sediments were performed such as total organic carbon (TOC) and grain size) and (iv) information were provided on the local most important contaminant source and their management. Only the two first criteria were discriminating.

Four types of contaminants were selected for this work, according physico-chemical properties allowing potential ionization. IOCs are classically considered as more soluble and more polar than non-ionizable ones, due to chemical moiety fine-tuned with water. However, in the four group of selected molecules, two can be considered as rather hydrophilic molecules (i.e. pesticides and pharmaceuticals) and two amphiphilic (i.e. PFAS and surfactants). This distinction if very important as amphiphilic molecules both have hydrophobic chain with C-C of C-F bondings and polar heads, generally with permanent charges, whereas pesticides and pharmaceuticals didn't display this hydrophobic chain. This is highlighted by the gap between two descriptors of molecule properties, log K<sub>ow</sub> and log D. While the former is estimated based on the lipophilicity of a molecule without taking into account its ionization state, the latter consider this. As a result, for PFOS, log D and log K<sub>ow</sub> are respectively 0.7 and 7.0 highlighting the impact of used parameter to assess the hydrophobicity of an amphiphilic compound whereas these values are -0.5 and 2.5 for tramadol (Table 1), which is much closer. It therefore emphasizes that theoretical values are questionable. A final theoretical or experimental descriptor of the affinity of IOCs with suspended particles is illustrated by the organic carbon partition coefficient (K<sub>OC</sub>, Table 1). The reported values varied significantly, as previously noted, highlighting the current limitations of such values in predicting the solid-water partitioning of IOCs.

PFAS, pesticides, pharmaceuticals and surfactants were selected as they bear permanent or amphoteric charges modifying their environmental fate and sedimentary occurrence. The sources of these molecules is mostly urban and point-source associated, especially for pharmaceuticals and surfactants that are considered pseudo-persistent, whereas pesticides are mostly associated with agricultural activities and PFAS sources are diverse.

## 3. Results

### 3.1. A reliable matrix?

Before discussing the representativity of contamination levels in sediment, it is important to note that research is conducted on various types of sediments, each with inherently distinct strengths and weaknesses. Most studies on IOC in sediment, as well as broader pollutants such as trace metals and persistent organic pollutants (POPs), have been performed on lacustrine and marine records. These environments are considered less disturbed by punctual events that could resuspend deposited materials and are therefore more suitable for historical reconstruction.

In contrast, riverbed and estuarine deposits are less stable, with frequent erosion and resuspension events, such as those occurring during floods, affecting the regularity of sediment deposition. This can lead to the formation of massive, instantaneous sediment layers or sedimentary hiatuses. While riverbeds are often located close to contamination sources and urban areas, identifying suitable sampling sites for sediment accumulation remains challenging due to variations in river history and management. As a result, sediment cores are often taken from riverbanks, where flood deposits (i.e., a major contributor to sediment deposition) accumulate, or from intermittently connected channels with lower water flow. These areas allow the deposition of finer particles and are generally considered more representative of
<caption>**Table 1**</caption>

Physico-chemical properties of some IOCs under investigation, with M<sub>w</sub> the mass weight in g.mol<sup>-1</sup>, pK<sub>a</sub> the dissociation constant of acid<sup>a</sup> of base<sup>b</sup>, K<sub>oc</sub> the organic carbon distribution coefficient, K<sub>ow</sub> the octanol-water distribution coefficient, D the ionization corrected octanol-water partition at a specific pH value, and S<sub>w</sub> the water solubility at 25 °C. Data gathered from chemspider.com.

<table><thead><tr><th>IOC Types</th><th>Molecule</th><th>M<sub>w</sub></th><th>pK<sub>a</sub><sup>a</sup></th><th>pK<sub>a</sub><sup>b</sup></th><th>Ionization State</th><th>Log K<sub>oc</sub></th><th>Log K<sub>ow</sub></th><th>Log D</th><th>S<sub>w</sub></th></tr></thead><tbody><tr><td rowspan="3">Pharm.</td><td>Acetaminophen</td><td>151.16</td><td>9.6</td><td>0</td><td></td><td>1.59</td><td>0.46</td><td>0.40</td><td>7000</td></tr><tr><td>Diclofenac</td><td>295.16</td><td>4.2</td><td>-</td><td></td><td>1.87</td><td>4.20</td><td>1.37</td><td>2.37</td></tr><tr><td>Tramadol</td><td>263.37</td><td></td><td>9.4</td><td>+</td><td>0.74</td><td>3.01</td><td>0.52</td><td>1151</td></tr><tr><td rowspan="3">Pest.</td><td>Diflufenican</td><td>394.30</td><td>10.3</td><td>0.6</td><td>0</td><td>3.60</td><td>4.20</td><td>4.09</td><td>0.05</td></tr><tr><td>Glyphosate</td><td>169.07</td><td>-0.6</td><td>9.6</td><td>+/-</td><td>0.00</td><td>-3.40</td><td>-6.66</td><td>335,000</td></tr><tr><td>Imidacloprid</td><td>255.66</td><td></td><td>11.2</td><td>+</td><td>0.99</td><td>0.57</td><td>-0.29</td><td>610</td></tr><tr><td rowspan="3">PFAS</td><td>8:2FTAB</td><td>570.37</td><td>?</td><td>?</td><td>+/-</td><td>4.47</td><td>0.90</td><td>n.a.</td><td>104</td></tr><tr><td>PFOS</td><td>500.12</td><td>&lt;1</td><td></td><td>-</td><td>2.57</td><td>7.03</td><td>0.66</td><td>570</td></tr><tr><td>PFHxS</td><td>400.11</td><td>0.14</td><td></td><td>-</td><td>3.55</td><td>5.25</td><td>-0.54</td><td>6.2</td></tr><tr><td rowspan="3">Surf.</td><td>Linear alkylbenzene sulfonate</td><td>325.48 (C12)</td><td>&lt;1</td><td></td><td>-</td><td>4.05</td><td>2.92</td><td>n.a.</td><td>20.2</td></tr><tr><td>Benzalkonium chloride (QAC)</td><td>304.55 (C12)</td><td></td><td>&gt;14.0</td><td>+</td><td>5.43</td><td>2.93</td><td>n.a.</td><td>22.5</td></tr><tr><td>Cocamidopropyl Betaine</td><td>342.52</td><td>2.4</td><td>8.1</td><td>+/-</td><td>2.81</td><td>-1.28</td><td>n.a.</td><td>23,676</td></tr></tbody></table>

historical contamination [16].

A reliable approach to assessing the continuity and representative-ness of sedimentary deposits is to date them. For sediment dating over the past century, two main tracers have emerged: ¹³⁷Cs and ²¹⁰Pb. ¹³⁷Cs dating relies on identifying time markers, such as atmospheric nuclear fallout events (frequently confirmed by ²⁴¹Am) and the Chernobyl accident in 1986, to estimate sedimentation rates between these reference points [17]. In contrast, ²¹⁰Pb dating uses isotopic lead decay [18], offering a more gradual approach by comparing supported and unsupported fractions through ²²⁶Ra assessment [19]. Both methods have their own limitations and are often combined to achieve the most

accurate dating [20] and to model sedimentation rates, which are essential for estimating sediment fluxes and understanding historical contamination.

However, these methods were primarily developed for undisturbed sedimentary columns, which is not always the case depending on the sampled environment. As a result, absolute dating is subject to significant errors, which must be taken into account when determining the first occurrence of specific contaminants, for example.

<caption>**Table 2**</caption>

Extraction methods according to the molecular targets in sedimentary archives. Bold numbers corresponded to molecular groups rather than specific targets (i.e., for surfactants).

<table><thead><tr><th>Targets</th><th>Area</th><th>Extraction</th><th>Solvents</th><th>Parameters</th><th>Cleanup</th><th>n<sub>IOC</sub></th><th>Reference</th></tr></thead><tbody><tr><td rowspan="3">Surfactants</td><td>Lake</td><td>Ultra sound Assisted Extraction</td><td>MeOH</td><td>30 min</td><td></td><td>2</td><td>[29]</td></tr><tr><td rowspan="3">Marine</td><td></td><td>MeOH: HCl</td><td>50 °C, 3 × 30 min</td><td></td><td>12</td><td>[30]</td></tr><tr><td></td><td>MeOH:HCl</td><td>60 °C</td><td></td><td>1</td><td>[31]</td></tr><tr><td></td><td>MeOH: HCl</td><td>60 °C/1h (x3)</td><td></td><td>2</td><td>[22]</td></tr><tr><td rowspan="5">Pesticides</td><td>Lake</td><td>Soxhlet</td><td>Hex:MeOH</td><td>20 h</td><td></td><td>4</td><td>[32]</td></tr><tr><td rowspan="3">Lake</td><td>Pressurized Liquid Extraction</td><td>Hex: Ace</td><td>100 °C</td><td></td><td>8</td><td>[33]</td></tr><tr><td></td><td>DCM</td><td></td><td></td><td>6</td><td>[34]</td></tr><tr><td></td><td>Ace:EtOAc:H<sub>3</sub>PO<sub>4</sub></td><td>80 °C/120 °C (130 bars)</td><td></td><td>66</td><td>[35]</td></tr><tr><td rowspan="3">Marine</td><td>Solid Liquid Extraction</td><td>KOH</td><td>1 min</td><td></td><td>2</td><td>[36]</td></tr><tr><td>River</td><td>Microwave Assisted Extraction</td><td>Acet:Hex:Cu</td><td>100W</td><td>Black Carbon/ Amine</td><td>12</td><td>[37]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="4">Pesticides + Pharmaceuticals.</td><td>Lake</td><td>Solid Liquid Extraction</td><td>AcN:NaCl:MgSO<sub>4</sub></td><td></td><td>C18</td><td>71</td><td>[26]</td></tr><tr><td rowspan="3">River</td><td>Ultra sound Assisted Extraction</td><td>DCM:MeOH</td><td>15 min</td><td>Silica gel/Na<sub>2</sub>SO<sub>4</sub></td><td>31</td><td>[38]</td></tr><tr><td>Pressurized Liquid Extraction</td><td>MeOH:EDTA</td><td>70 °C (100 bars)</td><td>HLB</td><td>41</td><td>[39]</td></tr><tr><td></td><td></td><td></td><td></td><td>41</td><td>[24]</td></tr><tr><td rowspan="3">Pharmaceuticals</td><td>Lake</td><td>Ultra sound Assisted Extraction</td><td>AcN:MeOH:EDTA</td><td>40 kHz (10 min)</td><td></td><td>20</td><td>[40]</td></tr><tr><td rowspan="2">Marine</td><td>Solid Liquid Extraction</td><td>EtAc:MeOH + MeOH:H<sub>2</sub>O</td><td>30,000 osc.min</td><td></td><td>6</td><td>[41]</td></tr><tr><td>River</td><td></td><td></td><td></td><td>1</td><td>[42]</td></tr><tr><td rowspan="10">PFAS</td><td rowspan="3">Marine</td><td>Pressurized Liquid Extraction</td><td>H<sub>2</sub>O:MeOH</td><td>100 °C</td><td>HLB</td><td>61</td><td>[43]</td></tr><tr><td>River</td><td>H<sub>2</sub>O:MeOH</td><td>100 °C (100 bars)</td><td></td><td>8</td><td>[44]</td></tr><tr><td></td><td>MeOH:H<sub>3</sub>PO<sub>4</sub>:NaOH</td><td></td><td></td><td>6</td><td>[45]</td></tr><tr><td rowspan="3">Lake</td><td>Ultra sound Assisted Extraction</td><td>MeOH:NaOH</td><td></td><td>Envi-Carb, WAX</td><td>14</td><td>[23]</td></tr><tr><td></td><td>MeOH:Cu</td><td>60 °C (30 min)</td><td>WAX</td><td>17</td><td>[46]</td></tr><tr><td></td><td>AcN</td><td>1h</td><td></td><td>44</td><td>[47]</td></tr><tr><td rowspan="3">Lake</td><td>Microwave Assisted Extraction</td><td>MeOH:EDTA</td><td>30 min</td><td>Strata-X</td><td>24</td><td>[26]</td></tr><tr><td></td><td>MeOH: AceOH</td><td></td><td>HLB</td><td>22</td><td>[48,49]</td></tr><tr><td></td><td>MeOH:NaOH</td><td></td><td></td><td>26</td><td>[50]</td></tr><tr><td rowspan="3">Marine</td><td>Solid Liquid Extraction</td><td>MeOH:NaOH</td><td>30 min</td><td>Envi-Carb</td><td>12</td><td>[51]</td></tr><tr><td rowspan="2">Ultra sound Assisted Extraction</td><td>MeOH: AceOH</td><td>50 °C, 30 min</td><td>WAX</td><td>23</td><td>[52]</td></tr><tr><td></td><td>MeOH:NaOH</td><td>30 min</td><td>Envi-Carb</td><td>20</td><td>[53]</td></tr><tr><td rowspan="4">Marsh</td><td rowspan="3">River</td><td>Ultra sound Assisted Extraction</td><td>EtOH:TBA</td><td></td><td>Envi-Carb</td><td>24</td><td>[54]</td></tr><tr><td></td><td>MeOH</td><td></td><td></td><td>16</td><td>[55]</td></tr><tr><td></td><td>MeOH:NaOH</td><td></td><td>Envi-Carb</td><td>9</td><td>[56]</td></tr><tr><td></td><td>Microwave Assisted Extraction</td><td>Hex: Ace</td><td>30 min</td><td>Envi-Carb</td><td>24</td><td>[57]</td></tr><tr><td rowspan="3">All</td><td rowspan="3">Marine</td><td>Solid Liquid Extraction</td><td>MeOH:CH<sub>3</sub>COONH<sub>4</sub></td><td>70 °C (100 bars)</td><td>Glass Wool/Graph. C</td><td>4</td><td>[58]</td></tr><tr><td rowspan="2">Pressurized Liquid Extraction</td><td>MeOH</td><td>70 °C (5 min)</td><td>Envi-Carb</td><td>34</td><td>[39]</td></tr><tr><td>TBA:Na<sub>2</sub>CO<sub>3</sub></td><td>30 min</td><td></td><td>22</td><td>[59]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>7</td><td>[25]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>124</td><td>[28]</td></tr></tbody></table>
## 3.2. Sediment extraction

Once properly sampled and dated, sediments must be extracted to solubilize target contaminants, as quantification is only possible in the liquid phase. Once some methods only use the affinity of molecules for organic solvents less polar than water combined with modified chemical conditions, such as solid-liquid extraction (Table 2), most of the methods for extracting compounds of interest remain the same: energy is applied to the sample to promote the desorption of molecules such as ultrasound assisted extraction and pressurized liquid extraction [21]. Energy input is achieved through three main technologies: ultrasound, microwaves, or pressurized liquid extraction. Higher temperatures are also frequently used to shift chemical equilibria, as they consistently promote desorption regardless of the adsorption mechanism.

However, achieving optimal recovery rates for a broad range of IOCs through solvent extraction and energy input only is not systematic. This is why additional IOC-specific chemical modifications are often applied and sometimes combined. Beyond the choice of solvent mixture (typically methanol with another chemical), several strategies have been used to improve analyte recoveries. A first approach consists in controlling and stabilizing the extraction pH in order to maintain a defined ionization state and thereby limit the analyte-matrix interaction. For example, for cationic IOCs, acidification (e.g., HCl or $H_3PO_4$ addition) reduces matrix proton-acceptor sites, decreasing interactions with positively charged analytes [22]. Conversely, for anionic species such as several PFAS, the use of alkaline conditions (e.g., NaOH) can reduce their affinity for negatively charged matrix components [23].

When the target list includes compounds with diverse ionization states, the objective shifts toward achieving acceptable recoveries across the full range, rather than optimizing for a single chemical class. In such cases, instead of drastically buffering the pH, the use of chelating agents (e.g., EDTA) or ion-pairing agents (e.g., TBA) has been proposed [24, 25]. These additives help reduce matrix complexity by complexing interfering ions of forming extractable ion-pairs, without excessively altering the sediment matrix itself. Nevertheless, among the reviewed studies (Table 2), 19 didn't employ any such chemical enhancement, while still achieving adequate recoveries. This variability makes it challenging to derive a comprehensive understanding of the specific added value of each methodological component.

It is also worth noting that extraction methods remain poorly standardized in the literature, with considerable variations in operational conditions (e.g. temperature, pressure). While the three main techniques, namely ultrasound-assisted, microwaves and pressurized-liquid extractions, are predominant, newer and more frugal methods are emerging, such as QUECHERS or ion-pairing extraction [26]. The extraction method itself does not appear to be specific to the compounds of interest, whereas the presence of a clean-up step in the extract is much more specific [27]. For instance, studies analyzing PFAS almost always include a clean-up step using solid-phase extraction (i.e., WAX or ENVI-Carb phases), while pharmaceutical and pesticide studies typically use HLB for this step, and surfactant studies often omit it entirely (Table 2).

Studies that do not focus on a particular family of molecules and perform only an extraction step generally opt for the least selective method possible and avoid the clean-up step [28]. This is a key element for adapting to the future potential of non-targeted analysis in sediment matrices. The quantification of molecular targets, normalized to the extracted dry mass of sediments, is adjusted based on the polarity and volatility of the targets, making it independent of the specific matrix being analyzed.

## 3.3. IOC quantification and validation procedure

While the extraction step, followed by any necessary purification, makes it possible to obtain an extract in which the target compounds are theoretically concentrated, we will focus here on the quantification of

the molecules themselves and on the validation of this quantification. Although practices have long been heterogeneous, the quantification of IOCs shares common features, at least within major compound families. Because of their ionizable and moderately polar character (Table 1), nearly all collected experiments rely on liquid chromatography, a soft ionization source (i.e., electrospray) and primarily tandem mass spectrometers for quantification (Table 3).

The only nuances are; (i) the source polarity, which is generally negative for PFAS analysis and positive for other molecules. However, several studies either inject the extracts twice, once in ESI+ and once in ESI-, to maximize analytical performance across all ionization states, or sometimes perform simultaneous analysis in ESI+ and ESI- (with a polarity switch), which degrades analytical performance but saves laboratory time; and (ii) the type of chromatographic column used, which is exclusively reversed-phase LC, with either apolar columns (C8 or C18 type) for surfactants and PFAS, or grafted and slightly more polar columns to enhance retention of hydrophilic molecules such as certain pharmaceuticals and pesticides. These different analytical practices, linked to specific types of compounds in routine protocols, are therefore quite specialized with respect to given ionization or hydrophobicity profiles. Unsurprisingly, non-targeted approaches developed for these matrices have largely aligned with these prerequisites, i.e., with compounds for which both the extraction and the analytical method were suitable [35].

One step for which the studies are markedly less consistent is analytical validation. While most studies use isotopically labelled internal standards (ILIS) to assess losses during the extraction procedure and to compensate for potential matrix effects, several studies use no internal standards at all (e.g., Refs. [38,58]), or rely solely on surrogate standards (e.g., Refs. [31,43]). Consequently, it is often difficult to evaluate specifically matrix effects in the absence of surrogate standards, as procedural ILIS gather extraction losses and matrix effects, and likewise, analytical validation in studies with only surrogate standards are fragile regarding potential heterogeneity during the extraction procedure, and when no ILIS are used, validation remains weak even when recovery ratios are determined from spiked pristine samples. In particular, variability in geochemical composition (organic matter content, grain size) can strongly influence recoveries as well as associated matrix effects [40]. It is therefore recommended to use at least one surrogate standard and as many ILIS as necessary (i.e., for each major chemical structure class) to account for the potential impact of these variations on quantification.

Finally, the determination of LQs, often performed using spiked matrix match samples, and the choice of spiking levels, which are generally consistent although one or two orders of magnitude higher than concentrations observed in environmental archives, are also far from harmonized. There is substantial variability in spiking levels (even within the same IOC groups), in the replicate number and in the matrices used. As a result, comparing limits of quantification across studies is challenging, although LQs are generally on the order of $pg g^{-1}$ for PFAS and two to three orders of magnitude higher for pesticides, pharmaceuticals, and surfactants (Table 3).

## 3.4. Occurrences and historical patterns

The four investigated IOC types are assumed to be exclusively generated by human activities, and their presence in sediment serves as an environmental tracer of their use within the watershed. Before discussing the potential quantitative applications in terms of temporal contamination trends, an initial presence/absence assessment allows us to assume that if an IOC is quantifiable in sediment, it must have been present in the water phase at the time of deposition. Due to the hydrophilic or amphiphilic nature of such IOCs, their absence in sediments indicates limited or no water contamination.

Based on this assumption, several studies have compared the market authorization date of IOCs, particularly pharmaceuticals and pesticides,
<caption>**Table 3**</caption>

Analytical performances and protocols for IOC assessment in sedimentary archives. With ILIS for isotopically labelled internal standard (bold numbers for surrogates added after extraction), [Spiking] the spiking concentration of ILIS (before extraction if available or after), Recovery the estimation method of Recovery ratio with Abs. for absolute (native compound) and Rel. for relative (internal standard correction), Performance with the number of investigated extraction replicates and the RSD in % (best-worse), and for source & for simultaneous polarity switch and/for dual injections, LQ for limit of quantification, LD for limit of detection and IDL for instrumental detection limit, n.p. for not provided.

<table><thead><tr><th>Targets</th><th>n<sub>IOC</sub></th><th>n<sub>ILIS</sub></th><th>[Spiking] ng g<sup>-1</sup></th><th>Recovery</th><th>Performance RSD (%)</th><th>Column</th><th>Source</th><th>Device</th><th>LQ (LD, IDL) ng g<sup>-1</sup></th><th>Reference</th></tr></thead><tbody><tr><td rowspan="3">Surf.</td><td>4</td><td>0</td><td>-</td><td>Abs.</td><td>n = 3, 5-8</td><td>C8</td><td>ESI+</td><td>DAD</td><td>4</td><td>[32]</td></tr><tr><td>12</td><td>1(1)</td><td>500</td><td rowspan="2">Rel.</td><td>n = 2, &lt;10</td><td rowspan="2">C18</td><td>ESI+</td><td>MS<sup>2</sup></td><td>5.0-30.0 pg g<sup>-1</sup></td><td>[22]</td></tr><tr><td>1</td><td>(1)</td><td>n.p.</td><td>n.p., 20</td><td>TOF-MS</td><td>n.p.</td><td>[31]</td></tr><tr><td rowspan="12">PFAS</td><td>20</td><td>7</td><td>0.2</td><td rowspan="12">Rel.</td><td>n = 3, 0.1-13</td><td rowspan="12">C18/polar C18</td><td rowspan="12">ESI-</td><td rowspan="12">MS<sup>2</sup></td><td>0.4-1.9 pg g<sup>-1</sup></td><td>[53]</td></tr><tr><td>24</td><td>8</td><td>0.5</td><td>n = 2, 4-25</td><td>0.02-0.09 pg g<sup>-1</sup></td><td>[54]</td></tr><tr><td>14</td><td>9</td><td>0.5</td><td>n = 3, 1-10</td><td>0.05-0.25</td><td>[23]</td></tr><tr><td>18</td><td>9</td><td>2</td><td>n.p.</td><td>0.0-0.7</td><td>[49]</td></tr><tr><td>26</td><td>16(1)</td><td>0.33</td><td>n.p.</td><td>0.05-1.0</td><td>[50]</td></tr><tr><td>22</td><td>10</td><td>1</td><td rowspan="2">Abs. & Rel.</td><td>n = 3, 1-27</td><td rowspan="2">C18</td><td rowspan="2">qTOF-MS</td><td rowspan="2">MS<sup>2</sup></td><td>0.01-0.49</td><td>[59]</td></tr><tr><td>23</td><td>15(9)</td><td>1</td><td>n = 5, 2-8</td><td>1-9 pg g<sup>-1</sup></td><td>[52]</td></tr><tr><td>7</td><td>1</td><td>2</td><td rowspan="4">Rel.</td><td>n = 2, 2-4</td><td>0.01-0.03</td><td>[25]</td></tr><tr><td>17</td><td>4</td><td>0.5</td><td>n = 5, 4-12</td><td>0.2-1.8 pg g<sup>-1</sup></td><td>[46]</td></tr><tr><td>16</td><td>8</td><td>n.p.</td><td>n = 7, n.p.</td><td>2.0-10.0 pg g<sup>-1</sup></td><td>[55]</td></tr><tr><td>9</td><td>2</td><td>3.3</td><td>n = 5, 0-4</td><td>0.03-1.0</td><td>[56]</td></tr><tr><td>44</td><td>7</td><td>n.p.</td><td rowspan="3">Rel.</td><td>n = 5, 2-14</td><td rowspan="3">C8<br>polar C18</td><td rowspan="3">ESI ±<br>ESI ±</td><td rowspan="3">qTOF-MS<br>MS<sup>2</sup></td><td>0.1-2</td><td>[47]</td></tr><tr><td>34</td><td>20</td><td>1</td><td>n = 3, 1-27</td><td>0.001-0.10</td><td>[39]</td></tr><tr><td>4</td><td>0</td><td>-</td><td>n = 3, 6-17</td><td>0.1-3</td><td>[58]</td></tr><tr><td rowspan="12">PFAS<br>Pharm.</td><td>6</td><td>1</td><td>-</td><td rowspan="12">Abs.</td><td>n = 5, 7-31</td><td rowspan="12">C18</td><td rowspan="12">ESI+</td><td rowspan="12">MS<sup>2</sup></td><td>1.0-40.8</td><td>[45]</td></tr><tr><td>61</td><td>(36)</td><td>~50</td><td>n = 3, &lt;15</td><td>0.3-2.1</td><td>[43]</td></tr><tr><td>13</td><td>3</td><td>n.p.</td><td>n = 6, &lt;6</td><td>0.3-3.0</td><td>[60]</td></tr><tr><td>8</td><td>0</td><td>-</td><td rowspan="2">Abs.</td><td>n = 3, 2.6-13</td><td rowspan="2">polar C18</td><td rowspan="2">ESI+</td><td>0.17-1.31</td><td>[44]</td></tr><tr><td>20</td><td>5(4)</td><td>200</td><td>n = 23, 0-258</td><td>0.3-22.4</td><td>[40]</td></tr><tr><td>1</td><td>1</td><td>500</td><td rowspan="2">Rel.</td><td>n = 6, n.p.</td><td>0.05</td><td>[42]</td></tr><tr><td>31</td><td>0</td><td>-</td><td>n.p., 0-20</td><td>0.1-14.1</td><td>[38]</td></tr><tr><td rowspan="2">Pharm.</td><td>42</td><td>15</td><td>100</td><td rowspan="2">Rel.</td><td>n = 3, 1-21</td><td rowspan="2">C18<br>polar C18</td><td rowspan="2">ESI+</td><td rowspan="2">MS<sup>2</sup></td><td>0.03-14.3</td><td>[24]</td></tr><tr><td>42</td><td>15</td><td>50</td><td>n = 3, 1-21</td><td>0.03-14.3</td><td>[39]</td></tr><tr><td>Pest.</td><td>66</td><td>0(19)</td><td>30</td><td rowspan="2">Rel.</td><td>n = 4, 2-24</td><td rowspan="2">C18<br>polar C18</td><td rowspan="2">ESI ±<br>ESI-</td><td rowspan="2">HR-MS<br>MS<sup>2</sup></td><td>0.06-0.63</td><td>[35]</td></tr><tr><td>Pest.</td><td>2</td><td>2</td><td>2</td><td>n = 3, 8-32</td><td>30-60</td><td>[36]</td></tr></tbody></table>

for which these dates are well-documented, with their first occurrences in sediment. These studies have generally found a strong correlation between the two (Table 4). In some cases, a time lag between market authorization and the first sedimentary detection has been observed, which is explained by the progressive increase in the molecule's usage over time [40]. These first occurrence assessments have also been used to cross-validate sediment dating with isotopic methods, often showing good agreement [43].

While most of the targeted compounds were introduced after World War II, this period also saw improvements in wastewater collection and treatment, as well as the implementation of primary environmental regulations in certain countries. A thorough understanding of the watershed is therefore essential when analyzing the historical trends of a specific molecule. It is crucial to distinguish between trends driven by the molecule's usage and those influenced by wastewater management (particularly for pharmaceuticals, PFAS, and surfactants) in order to accurately interpret historical contamination patterns (Table 4).

For example, most studies analyzing surfactant occurrences in sedimentary archives have identified a similar pattern: an increasing trend in sediment contamination until the 1980s or 1990s, followed by a decline [22,30]. However, this recent decrease does not necessarily indicate a reduction in surfactant use but rather reflects the increasing efficiency of wastewater treatment. Despite their high concentrations in wastewater, surfactants are effectively removed during treatment, significantly limiting their environmental presence. Thus, sedimentary archives capture both wastewater management practices and historical usage trends.

A similar pattern is often observed for other point-source contaminants of concern, as improvements in wastewater treatment enhance the removal of degradable contaminants. However, the situation is different for PFAS. The sedimentary concentration peak for PFAS generally occurs later than for pharmaceuticals or surfactants, highlighting their more

persistent nature. This suggests that wastewater management alone is not sufficient to explain PFAS contamination patterns, and additional factors must be considered [61]. The complex degradation pathways of PFAS, along with the potential contribution of localized contamination sources, make global assessments challenging. Nevertheless, an overall decline in PFAS contamination has been observed since the 2000s [56, 59], largely due to regulatory actions targeting "legacy" PFAS compounds (e.g., PFOS, PFHxS, and PFOA). Regulations and modifications in industrial processes, initiated in the early 2000s, have contributed to this decline [61]. However, given the chemical diversity of PFAS and the widespread use of substitute compounds, the long-term outlook remains less optimistic, especially regarding the continuous atmospheric contamination recorded by remote lake sediments [52].

Pesticides are also affected, to a lesser extent, by improvements in the management of point sources due to the more diverse pathways through which they reach aquatic environments, primarily from agricultural sources. The observed temporal dynamics are therefore linked to their usage, which is sometimes influenced by bans, particularly since the 2000s for non-OCPs molecules [24], but also by the introduction of new molecules [35]. It should also be noted that environmental stocks of these molecules, particularly in soils, are gradually released into water bodies for highly persistent compounds, such as atrazine, and are also recorded in sediment archives [33]. Regulations have played a crucial role in shaping the historical distribution of pesticides. Cycles of authorization and bans, such as the restriction of triazines in Western Europe in the early 2000s and the significant reduction of non-agricultural pesticide use (excluding as biocides) since the 2010s, are well-documented in sedimentary records. For these compounds, which are less affected by wastewater treatment processes, the sequential replacement of widely used molecules is clearly visible in sediment archives. Additionally, gradual dose reductions prior to a complete ban of a specific compound are also recorded in sediment
<table><caption>**Table 4**

Reviewed studies following the criteria. In case of multiple cores in a same manuscript, the extreme values (length, age) were taken. Bold numbers in n<sub>IOC</sub> refers to molecular groups (i.e., for surfactants).</caption><thead><tr><th>Environ.</th><th>Country</th><th>Area (n<sub>cores</sub>)</th><th>Identified Sources</th><th>Length (cm)</th><th>Record</th><th>Datation</th><th>φ</th><th>TOC</th><th>Targets</th><th>n<sub>IOC</sub></th><th>Datation marker</th><th>Use record</th><th>Source management record</th><th>Major results</th><th>Ref.</th></tr></thead><tbody><tr><td rowspan="2">Marine</td><td rowspan="2">USA</td><td rowspan="2">Jamaica bay (2)</td><td rowspan="2">Sewage</td><td>66 cm</td><td>1938–2008</td><td><sup>137</sup>Cs<br/><sup>7</sup>Be</td><td>n.a.</td><td>2–7 %</td><td>Surf.</td><td>1</td><td>Yes</td><td>Yes</td><td>Yes</td><td>First appearance in 1940s and global maximum concentration during 1990s, but relay with one molecule in constant increase since</td><td rowspan="2">[31]</td></tr><tr><td>60 cm</td><td>1948–2008</td><td><sup>210</sup>Pb<br/><sup>137</sup>Cs</td><td></td><td>2–7 %</td><td>Pharm.</td><td>61</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Consistent first occurrences and increase in two cores, with global increase of diversity and total occurrences except for sulfamethazine and propranolol (relay with more recent active principles)</td><td rowspan="2">[43]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Surf.</td><td>12</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Global increase of occurrences until 1990s, except for 4 groups with decrease began since 1970s</td><td rowspan="2">[30]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Transition between LAS and TPS in 1960s highlighting in-situ degradation, and global increase of occurrences due to sewage pressure and use.</td><td rowspan="2">[32]</td></tr><tr><td>Italy</td><td>Venice Lagoon (1)</td><td>Sewage</td><td>&lt;100 cm</td><td>1910–1972</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>1 %</td><td>Surf.</td><td>4</td><td>Yes</td><td>Yes</td><td>Yes</td><td>PFOS is the only historical detected molecule (1950s) while strong diversification since 1980s and slight decrease since 2007</td><td rowspan="2">[53]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Global increase pattern with acceleration in the 1990s (following TOC evolution)</td><td rowspan="2">[55]</td></tr><tr><td>South-Korea</td><td>Jinhae Bay (4)</td><td>Mixed</td><td>83 cm</td><td>1941–2011</td><td><sup>210</sup>Pb</td><td>Silt</td><td>1–2.5 %</td><td>PFAS</td><td>16</td><td>No</td><td>Yes</td><td>No</td><td>Only PFOS was detected since 1950s with increasing trend until stabilization during the 2000s</td><td rowspan="2">[57]</td></tr><tr><td>Arctic</td><td>Bering sea (1)</td><td>Mixed</td><td>33 cm</td><td>1952–2015</td><td><sup>210</sup>Pb</td><td>Silt</td><td>~1 %</td><td>PFAS</td><td>9</td><td>Yes</td><td>Yes</td><td>No</td><td>Shift from PFOS-based products (continuous increase until 2000s) to telomere-based products</td><td rowspan="2">[54]</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>Distinction between historical contamination and contamination under concern in term of sedimentary occurrences.</td><td rowspan="2">[28]</td></tr><tr><td>USA</td><td>Strait of Juan de Fuca (4)</td><td>Mixed</td><td>220 cm</td><td>1896–2009</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>2 %</td><td>PFAS</td><td>24</td><td>Yes</td><td>Yes</td><td>No</td><td>Continuous increase of glyphosate and AMPA on one site, recent decrease on another attributed to local restrictions</td><td rowspan="2">[36]</td></tr><tr><td>Japan</td><td>Tokyo Bay (1)</td><td>Mixed</td><td>43 cm</td><td>1966–2004</td><td><sup>210</sup>Pb<br/><sup>137</sup>Cs</td><td>n.a.</td><td>2.5–4 %</td><td>PFAS</td><td>24</td><td>Yes</td><td>Yes</td><td>No</td><td>Sharp increase in both area from oldest layers, decrease from 1980s peak attributed to wastewater management. Temporal variation of BAC homologues.</td><td rowspan="2">[22]</td></tr><tr><td>USA</td><td>Palos Verdes (CA) (1)</td><td>Mixed</td><td>60 cm</td><td>&lt;1970–2007</td><td>DDT</td><td>n.a.</td><td>n.a.</td><td>PFAS<br/>Pharm.<br/>Pest.</td><td>124</td><td>No</td><td>No</td><td>No</td><td>Weak variation along the cores, age model without confirmation</td><td rowspan="2">[58]</td></tr><tr><td>France</td><td>Martinique Guadeloupe (2)</td><td>Agric.</td><td>110 cm</td><td>1940–2018</td><td><sup>210</sup>Pb<br/><sup>137</sup>Cs</td><td>Silt</td><td>15 %</td><td>Pest.</td><td>2</td><td>Yes</td><td>Yes</td><td>Yes</td><td></td><td></td></tr><tr><td>China</td><td>Pearl River Estuary</td><td>Sewage</td><td>75 cm</td><td>1950–2012</td><td><sup>210</sup>Pb<br/><sup>137</sup>Cs</td><td>n.a.</td><td>n.a.</td><td>Surf.</td><td>2</td><td>Yes</td><td>Yes</td><td>Yes</td><td></td><td></td></tr><tr><td>Japan</td><td>Tokyo Bay (2)</td><td>Sewage</td><td>40 cm</td><td>&lt;1960–&gt; 2000</td><td><sup>137</sup>Cs</td><td>n.a.</td><td>~5 %</td><td>PFAS<br/>Pharm.</td><td>4</td><td>No</td><td>No</td><td>No</td><td></td><td></td></tr></tbody></table>

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<table><caption>Table 4 (continued)</caption><thead><tr><th>Environ.</th><th>Country</th><th>Area (n<sub>cores</sub>)</th><th>Identified Sources</th><th>Length (cm)</th><th>Record</th><th>Datation</th><th>φ</th><th>TOC</th><th>Targets</th><th>n<sub>IOC</sub></th><th>Datation marker</th><th>Use record</th><th>Source management record</th><th>Major results</th><th>Ref.</th></tr></thead><tbody><tr><td rowspan="10">Lake</td><td>Spain</td><td>L'Albufera Lake (2)</td><td>Mixed</td><td>70 cm</td><td>-100 - recent</td><td><sup>14</sup>C</td><td>Sandy to silty</td><td>n.a.</td><td>PFAS Pharm. Pest.</td><td>132</td><td>No</td><td>No</td><td>No</td><td>Curious<sup>14</sup>C datation, in opposition with<sup>210</sup>Pb datation. Large diversity of contaminant detected, without temporal trends, even in postulated very old layers</td><td>[26]</td></tr><tr><td>Sweden</td><td>Lake Ekoln (2)</td><td>Sewage</td><td>55 cm</td><td>1950-2013</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>n.a.</td><td>Pharm.</td><td>6</td><td>Yes</td><td>Yes</td><td>No</td><td>Consistence between sale increase and sedimentary occurrences, except for diazepam and clonazepam</td><td>[41, 42]</td></tr><tr><td rowspan="2">Canada</td><td>Lake Ontario (2)</td><td>Mixed</td><td>35 cm</td><td>1954-2004</td><td><sup>210</sup>Pb</td><td>Fine</td><td>-</td><td>PFAS</td><td>14</td><td>Yes</td><td>Yes</td><td>No</td><td>Increase of PFAS flux particularly since 1980s, contamination of short and long-chain, use of EOF.</td><td>[23]</td></tr><tr><td>Lakes Opabin, Oesa (2)</td><td>Atmo.</td><td>24 cm</td><td>1700-2008</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>2-9 %</td><td>PFAS</td><td>12</td><td>Yes</td><td>Yes</td><td>No</td><td>First contamination in 1957, and increase since with close relative proportion of PFCA</td><td>[51]</td></tr><tr><td>USA</td><td>Lakes Pepin, Winona, Duluth Harbor (MI) (3)</td><td>Sewage Agric.</td><td>155 cm</td><td>1870-2010</td><td><sup>210</sup>Pb</td><td>Fine</td><td>10-40 %</td><td>Pharm.</td><td>20</td><td>Yes</td><td>Yes</td><td>No</td><td>Consistence for first quantifications, and relay between molecules of the same therapeutic group with increase of the newest</td><td>[40]</td></tr><tr><td>Sweden</td><td>Luleå (2)</td><td>Ind.</td><td>14 cm</td><td>&lt;1968-2009</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>0.50 %</td><td>PFAS</td><td>26</td><td>Yes</td><td>Yes</td><td>No</td><td>Strong and recent (2000s) increase of sum occurrences with historical major contributions of PFOS and PFHxS, recent diversification</td><td>[50]</td></tr><tr><td>France</td><td>Lake Saint-André (1)</td><td>Agric.</td><td>55 cm</td><td>1890-2015</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt</td><td>7.50 %</td><td>Pest.</td><td>6</td><td>Yes</td><td>Yes</td><td>No</td><td>Consistent first quantifications (but delayed) and global increase except for two fungicides, with recent decrease or disappearance without ban.</td><td>[34]</td></tr><tr><td>China</td><td>Lake Chaohu (3)</td><td>Mixed</td><td>20 cm</td><td>1952-2006</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt-clay</td><td>0.50 %</td><td>PFAS</td><td>17</td><td>No</td><td>Yes</td><td>No</td><td>Strong increase from 1950s to 1970s, stabilized since. Strong correlation with TOC for long-chained PFAS.</td><td>[46]</td></tr><tr><td rowspan="3">USA</td><td>Great lakes Ontario, Erie, St Clair (13)</td><td>Mixed</td><td>n.a.</td><td>1900-2012</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>2-12 %</td><td>PFAS</td><td>22</td><td>Yes</td><td>Yes</td><td>No</td><td>Overall and continuous increase of global contamination, particularly through PFBA, in parallel to TOC content.</td><td>[48]</td></tr><tr><td>Great lakes Superior, Huron, Michigan (20)</td><td>Mixed</td><td>18 cm</td><td>1880-2005</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>~4 %</td><td>PFAS</td><td>22</td><td>No</td><td>Yes</td><td>No</td><td>18 Compounds detected without a clear temporal distribution except for recent increase of PFBA and PFBS. No correlation with organic carbon content.</td><td>[49]</td></tr><tr><td>Great lakes Superior, Huron, Michigan (12)</td><td>Mixed.</td><td>18 cm</td><td>1830-2010</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>n.a.</td><td>Pest.</td><td>8</td><td>No</td><td>Yes</td><td>No</td><td>Regular increase of DEA/Atrazine ratio with maximal concentration in the 1990s. Early quantification of pesticides (before 1900s) explained by mobility.</td><td>[33]</td></tr><tr><td>Canada</td><td>Lakes Hazen and B35 (2)</td><td>Atm.</td><td>17 cm</td><td>1923-2011</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>n.a.</td><td>PFAS</td><td>23</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Exponential increase of flux due to snow melting, one of the major source of PFAS in such lake through atmospheric deposition.</td><td>[52]</td></tr><tr><td>Japan</td><td>Teganuma Lake (4)</td><td>Sewage</td><td>37 cm</td><td>1980-2000</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>2-3 %</td><td>Surf.</td><td>2</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Only LAS detected, site with frequent cleaning. Contamination reaching 1 mg.g-1, and reflecting well the</td><td>[29]</td></tr></tbody></table>

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<table><caption>Table 4 (continued)</caption><thead><tr><th>Environ.</th><th>Country</th><th>Area (n<sub>cores</sub>)</th><th>Identified Sources</th><th>Length (cm)</th><th>Record</th><th>Datation</th><th>φ</th><th>TOC</th><th>Targets</th><th>n<sub>IOC</sub></th><th>Datation marker</th><th>Use record</th><th>Source management record</th><th>Major results</th><th>Ref.</th></tr></thead><tbody><tr><td rowspan="4">River</td><td rowspan="2">Switzerland</td><td>Lake Moosse (1)</td><td>Agric.</td><td>55 cm</td><td>1924–2014</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>3.5–4.5 %</td><td>Pest.</td><td>66</td><td>Yes</td><td>Yes</td><td>No</td><td>wastewater effluent management over the 30 years of record.</td><td>[35]</td></tr><tr><td>Tyrifjorden Lake (1)</td><td>Ind.</td><td>30 cm</td><td>1934–2017</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Coarse silt</td><td>1–4 %</td><td>PFAS</td><td>44 (19)</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Most of the molecules quantified in agreement with market authorization. Relay between old banned molecules and newly marketed ones.</td><td>[47]</td></tr><tr><td rowspan="2">China</td><td>Haihe River (3)</td><td>Mixed</td><td>56 cm</td><td>1945–2010</td><td><sup>210</sup>Pb</td><td>n.a.</td><td>1–2 %</td><td>PFAS</td><td>7</td><td>No</td><td>?</td><td>No</td><td>High concentration of PFOS precursors due to local source (paper products) with good agreement between historical use and contamination profile.</td><td>[25]</td></tr><tr><td>Guangzhou/ Longyan (2)</td><td>Agri.</td><td>35 cm</td><td>1957–2012</td><td><sup>137</sup>Cs</td><td>n.a.</td><td>0.5–3 %</td><td>Pest.</td><td>12</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Sawtooth vertical distribution with major contributions of PFOS and PFDoA</td><td>[37]</td></tr><tr><td>Serbia</td><td>Danube (1)</td><td>Sewage</td><td>70 cm</td><td>&lt;3 yrs (1990s)</td><td><sup>137</sup>Cs</td><td>Silt</td><td>1–2 %</td><td>Pest. Pharm.</td><td>31</td><td>No</td><td>No</td><td>No</td><td>Relay between old (OCPs) and new contaminants of concern (fipronil, pyrethrinoids)</td><td>[38]</td></tr><tr><td rowspan="4">France</td><td rowspan="2">Seine River (1)</td><td>Mixed</td><td>95 cm</td><td>1950–2004</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>n.a.</td><td>4 %</td><td>Pharm.</td><td>6</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Decreasing pattern, consistent with fecal markers. Strong impact of flood on distribution</td><td>[45]</td></tr><tr><td>Loiret River (1)</td><td>Sewage</td><td>62 cm</td><td>1960–2003</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt</td><td>5 %</td><td>Pharm.</td><td>14</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Consistent first detections before increasing/decreasing pattern due to sewage management</td><td>[44]</td></tr><tr><td rowspan="2">Rhône River (1)</td><td>Ind.</td><td>140 cm</td><td>1977–2013</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt</td><td>0.2–3 %</td><td>PFAS</td><td>22</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Strong increase after the withdrawal of the major WWTP effluent source. Consistent first detections with MAD.</td><td>[59]</td></tr><tr><td>Seine River (1)</td><td>Mixed.</td><td>580 cm</td><td>1944–2003</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt-clay</td><td>6–12 %</td><td>Pest. Pharm.</td><td>41</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Strong increase until 2000s followed by decrease and change of molecular profile due to industrial activity changes</td><td>[24]</td></tr><tr><td>Seine River (1)</td><td>Mixed</td><td>206 cm</td><td>1945–2021</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt</td><td>5–10 %</td><td>PFAS Pest. Pharm.</td><td>76</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Shift during the 1980s and 2000s between triazines and new marketed molecules; a sharp decline of Pharm. since the introduction of more advanced treatment in 1997. Good historical consistency of first quantifications</td><td>[39]</td></tr><tr><td>Seine River (1)</td><td>Mixed</td><td>206 cm</td><td>1945–2021</td><td><sup>210</sup>Pb <sup>137</sup>Cs</td><td>Silt</td><td>5–10 %</td><td>PFAS Pest. Pharm.</td><td>76</td><td>Yes</td><td>Yes</td><td>Yes</td><td>First phase of increase, then decrease at different periods following ban of products (Pest., PFAS) or improved management of point sources (Pharm)</td><td>[39]</td></tr></tbody></table>
layers [39].

# 4. Discussion

## 4.1. A mirror of the aqueous contamination?

A challenging and not yet fully understood question is the quantitative relationship that may exist between sedimentary contamination and contamination in the aquatic compartment. Several studies have assumed that the historical distribution of IOCs within an archive follows the historical pattern of dissolved contamination, based on the premise that solid/water partitioning is the primary driver of sedimentary occurrence. This assumption appears valid for POPs, which are highly hydrophobic and resistant to degradation, but seems less applicable to IOCs.

The affinity of IOCs for sediment generally depends on key geochemical parameters such as grain size and clay content on one hand, and organic content on the other—particularly for amphiphilic compounds. While the interaction between POPs and sediment is predominantly driven by hydrophobic and electrostatic interactions (Fig. 1), which are largely controlled by organic content [62], the potential ionization of IOCs allows for additional types of interactions, such as cationic bridges or ion exchange, mostly cationic (anion exchange is less frequent but can occur, Figure) [63]. These interactions enable the selective sorption of organic molecules, even at low concentrations. Consequently, monitoring the evolution of at least grain size and organic content along the sedimentary profile is essential for estimating the historical sorption potential of sediments. This is particularly relevant in fluvial environments with flood deposits, which are generally coarser and contain less organic material than other layers (see Fig. 2).

Another key factor in understanding the quantitative relationship between both phases is the potential degradation of contaminants once trapped in sediment. Most authors agree that sorption significantly limits, or even halts, degradation processes such as biodegradation, photolysis, and hydrolysis. During the burial process, oxygen availability is often reduced, and degradation shifts from aerobic to anaerobic conditions. This is particularly relevant for biodegradation, which has been shown to occur more rapidly under aerobic conditions for most IOCs, such as pharmaceuticals [64] and surfactants [65]. Therefore, before reaching anaerobic or anoxic conditions, significant initial reductions in IOC content are likely due to aerobic biodegradation,

<figure><img src="image_1.png" /><figcaption>Fig. 2. Schematic representation of IOC contaminated sediment fate.</figcaption></figure>

especially for readily biodegradable contaminants like surfactants and some pharmaceuticals.

Finally, the potential mobility of IOCs in sediment columns remains a crucial question that has only been partially investigated. While some authors have mentioned mobility within the sediment column to explain contaminant detections slightly preceding their theoretical market release (though not strictly within the model's age margin of error), the prevailing assumption is often that mobility is negligible. However, this assumption may be overly simplistic, particularly in areas where the sediment column is in connection with groundwater.

Significantly earlier detections than market authorization dates are rarely reported in the literature and generally stem either from original dating methods applied to recent sediments [26] or from detections at low concentrations in environment with limited sedimentation rate [49], sometimes near the quantification limits, whose estimation remains uncertain. Therefore, no irrefutable evidence of IOC mobility, even postulated by the authors [33] within the sediment column has been provided. It is for example hard to believe that among a group of molecules, only one can be mobile in the sedimentary column due to a different structure. Moreover, numerous studies confirming the strong correlation between IOC detections or concentration trend variations following management events help to sidestep this issue, and also through sampling twice but after years the same site and compare the occurrences that were both in good agreement in term of concentration and historical distribution [31,42,43].

IOCs are often considered pseudo-persistent rather than truly persistent molecules, although certain compounds (e.g., PFAS, atrazine, and carbamazepine) have demonstrated remarkable persistence in environmental compartments. Back-calculating historical environmental concentrations from sedimentary occurrences requires a deeper understanding of burial processes, which may vary significantly between sampling sites.

## 4.2. Normalization possible beyond classical TOC

The advantage of sedimentary archives can also be one of their weaknesses, as the environmental conditions at the time of deposition are not fully understood. Fundamentally, using the solid/water partition coefficient has the advantage of being very simple and does not require additional data to estimate dissolved concentrations. However, these coefficients are not linear, as they depend on the amount of suspended solids [3] and geochemical characteristics. Since sedimentary deposition frequently occurs after flood events, characterized by higher suspended solids concentrations, the selection of a specific $K_d$ value remains unresolved, even though regular quantitative relationships have been observed for specific systems [1,66].

Moreover, precise knowledge of historical conditions, such as pH, is often lacking. This can be particularly problematic for IOCs with pKa values close to environmental pH, as slight modifications may significantly impact their affinity with solids. Because amphiphilic IOCs exhibit both hydrophilic and hydrophobic properties, organic carbon

<figure><img src="image_2.png" /><figcaption>Fig. 1. Interaction mechanisms between IOCs (circles) depending on their ionization state (blue for cationic, red for anionic and black for neutral) and the type of surfaces with organic matter in dark line and mineral surface as green crystalline structures. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>
normalization is the most commonly used method to determine whether contamination trends are due to changes in aqueous concentrations or sediment properties. However, particularly for strong and weak bases, such as most pharmaceuticals, the contribution of mineralogical composition to sorption cannot be entirely dismissed. This limitation is often minor, as fine-grained sediments, which are more reactive due to their higher specific surface area, typically correlate well with organic content, justifying this simplification.

TOC assessment may also be insufficient, as the sorption potential of IOCs is not constant across different types of organic matter. The widespread occurrence of microplastics, which can sometimes enhance the trapping of IOCs [67], along with other highly sorptive particles [68], further complicates the normalization process.

Finally, some authors have proposed using accumulation rates, rather than sedimentary occurrences in ng·g⁻¹ or TOC-normalized occurrences. This approach is particularly relevant in lacustrine environments, as it normalizes data to catchment size and sedimentation rate, providing a more accurate picture of the historical transfer of IOCs. This method assumes that IOCs are transported via suspended solids, such as those generated from soil erosion.

While studies on the historical occurrences of IOCs vary significantly in how they account for sediment geochemistry, performing organic carbon analysis remains essential, as it provides a direct basis for normalization. Other analyses, such as grain size distribution, are recommended but are currently challenging to use directly for interpreting historical IOC distributions, even though their impact is acknowledged.

### 4.3. What added values does this approach bring?

Despite the potential limitations mentioned above and the current challenges in achieving fully retrospective quantification, sedimentary archives remain a unique tool for evaluating historical IOC contamination. This potential is particularly valuable for documenting past contamination by IOCs, as research interest in these molecules only began in the 1990s, despite their market authorization occurring much earlier, and sale data are sparsely available particularly at local scale for such periods. Today, risk assessments of these compounds must consider their environmental persistence, and the quantification of various IOCs in older sediments plays a crucial role in this process, to inform on their environmental fate over a long period.

Sedimentary archives also provide insights into the time lag between market authorization and the first environmental detections. This delay can result from the gradual adoption of a substance by the population or the need for significant usage to reach detectable levels, particularly for compounds with unfavorable sorption properties (Fig. 3). Notably, for less hydrophilic IOCs, this time lag has often been observed to be

<figure><img src="image_3.png" /><figcaption>**Fig. 3.** From sedimentary archives to historical contamination trend, methods and potentials.</figcaption></figure>

minimal.

Furthermore, sedimentary records can highlight the extensive wastewater collection and treatment initiatives that began in industrialized countries in the 1970s. While initial efforts targeted carbonaceous organic matter and nutrients, they also had significant effects on the removal rates of IOCs. The step-by-step improvements in wastewater management can be traced through sedimentary archives, offering valuable insights into the evolution of treatment efficiency.

These archives can also complement traditional monitoring programs by documenting the impact of regulations, such as bans, on the environmental presence of certain compounds. While some molecules disappeared rapidly after being banned, others persisted for long periods, such as certain triazines or PFAS [50]. This persistence highlights the remobilization of environmental reservoirs of these substances, underscoring the need for ongoing surveillance [52].

Recent development of non-target screening techniques allows for the broader exploitation of information stored in sediments [69]. Rather than being limited to a predefined list of molecules, this approach enables a more comprehensive assessment of historical environmental contamination. Fully leveraging the unique ability of sedimentary archives to provide an integrated view of past contamination is essential for advancing environmental research and management, and particularly to track metabolites of used products, as even for very mobile and hydrophilic molecule and by-products [70], such as glyphosate and AMPA, both can be detected in sediments [34]. However, extraction methods have to be adapted and avoid purification steps that were considered necessary due to the weak occurrences of some target molecules and to assure their proper quantification is such complex matrix. A balance has therefore to be made between selectivity and sensibility [71].

### 4.4. What is the real chemical diversity captured in sediments?

A central message emerging from recent work on ionized organic contaminants in sedimentary archives is that the chemical diversity we observe is largely shaped, and often constrained, by analytical limitations [69,72]. Sediments are among the most complex matrices encountered in environmental analysis, rich in natural organic matter, lipids, pigments, and diverse inorganic constituents [73]. These components generate pronounced matrix effects that influence ionization efficiency, inflate background noise, and obscure low-abundance signals. As a result, contaminants can be missed entirely, while non-target workflows, when used, frequently produce artefactual features that require extensive manual verification. These issues are particularly acute in full-scan LC-HRMS datasets, where limited fragmentation specificity increases the risk of misassigning natural compounds as contaminants. Matrix effects vary strongly across chemical classes. Specifically, IOCs interact extensively with dissolved organic matter and inorganic ions. Commonly used strategy to reduce suppression, such as dilution, invariably reduces sensitivity for trace-level analytes. No broadly accepted correction framework exists, contributing to significant variability in analytical coverage across laboratories.

Internal standard availability further shapes what can be confidently quantified or confirmed. Isotopically labelled standards remain scarce for many IOCs and are often prohibitively expensive. Semi-quantification using structurally analogous surrogates is widespread but intrinsically less reliable: differences in polarity, ionization behavior, and chromatographic retention introduce large uncertainties and hinder inter-study comparability, that can be partially overcome in target screening by the use of qualification transition, or specific fragments in qTOF-MS. The development of internal standard panels that better span the chemical space of ionizable contaminants is therefore a critical unmet need.

Identification is similarly constrained by instrumentation and library coverage, particularly in non-target screening. While LC-HRMS enables broad detection of features, annotation confidence depends on
acquisition strategy, fragmentation quality, and the availability of reference spectra [71,74]. Existing libraries cover only a fraction of relevant contaminant classes, limiting the ability to reach high confidence levels. Although the Schymanski framework has improved reporting consistency [75], it cannot compensate for variability in resolution, collision energies, or spectral completeness, which continue to hinder cross-study harmonization.

Together, these limitations create substantive blind zones in sediment analysis. Many IOCs appear in only a handful of studies despite their potential ecological relevance suggesting analytical underrepresentation rather than true environmental scarcity. Improving matrix-effect mitigation, expanding internal standard resources, advancing ionization and fragmentation strategies, and building more comprehensive HRMS databases will be essential steps toward revealing the true chemical complexity archived in sediments.

## 5. Conclusion and future prospects

Sedimentary archives serve as effective tools for reconstructing the historical dynamics of IOCs in aquatic environments. Despite the complex and less predictable interactions of IOCs with sediments, that are governed by factors such as organic carbon content, mineralogy, pH, and redox conditions, sediment records have proven valuable for tracking temporal trends in contamination. These archives reveal clear signals of anthropogenic influence on environmental compartments, sometimes including time lags between compound introduction and environmental detection, and the effects of regulatory actions and improvements in wastewater treatment practices. While direct quantification of past dissolved-phase concentrations remains challenging, the relative evolution of contamination is well supported by sediment data.

Future research should aim to refine sediment-based reconstructions by improving dating accuracy for example by using IOC as chronomarkers, integrating mineralogical and grain-size analyses for advancing normalization techniques to better account for amphiphilic and hydrophilic IOCs, and improving confidence in the possible quantitative link between sediment contamination level and historical contamination. The inclusion of non-target screening approaches can expand the scope of analysis, uncovering emerging or previously undetected contaminants. Importantly, progress in these domains will depend on tackling the analytical challenges highlighted in this review related to both target and non-target screening. Standardized extraction protocols, improved control of matrix effects, expanded availability of internal standards, and more comprehensive HRMS libraries are essential for ensuring comparability across studies and for maximizing the information extracted from sedimentary archives. To fully exploit the potential of sedimentary archives, standardized analytical protocols both at the extraction and analysis steps are essential. Such efforts will help translate sediment insights into effective regulatory and monitoring strategies, as a support for stakeholders and enhancing our long-term understanding of chemical pollution.

## 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.

## Data availability

Data will be made available on request.

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