1 CORBICULA FLUMINEA: A SENTINEL SPECIES FOR URBAN RARE EARTH ELEMENT ORIGIN

2 Clément PERETO (clement.pereto@gmail.com)¹, Alexandra COYNEL (alexandra.coynel@u-

3 bordeaux.fr)¹*, Antoine LERAT-HARDY (antoine.lerat@u-bordeaux.fr)¹, Pierre-Yves

4 GOURVES (pierre-yves.gourves@u-bordeaux.fr)¹, Jörg SCHÄFER (jorg.schafer@u-

5 bordeaux.fr)¹ and Magalie BAUDRIMONT (magalie.baudrimont@u-bordeaux.fr)¹.

6 Author Information

7 1: Université de Bordeaux- UMR CNRS 5805 EPOC ; Allée Geoffroy Saint Hilaire Bât NB18

8 - CS 50023, 33615 PESSAC CEDEX, FRANCE.

9 Corresponding Author

10 Tel: 33 (0)5 40 00 88 38

11 Email: alexandra.coynel@u-bordeaux.fr

12 Permanent address: UMR CNRS 5805 EPOC – OASU, Université de Bordeaux, Site de

13 Talence – Bâtiment B18N, Allée Geoffroy Saint-Hilaire, CS 50023, 33615 PESSAC CEDEX,
14 France.

15 **Notes**

16 The manuscript was written through contributions of all authors. All authors have given

17 approval to the final version of the manuscript. The authors declare no competing financial

18 interest.
1 Abstract

The increase in the global population, coupled with growing consumption of Rare Earth Elements (REEs), has led to increasing transfer of these emerging contaminants into the environment, particularly through the effluents from wastewater treatment plants (WWTP). The objectives of this study were to determine the geochemical quality of a French river subject to strong urban pressure (the Jalle River in the Bordeaux area) and to examine the bioavailability of natural and anthropogenic REEs in a model species of freshwater bivalve, the Asian clam *Corbicula fluminea*.

To this end, two fractions (dissolved and total) of the water from the Jalle River were sampled and the bivalves were exposed by *in situ* caging during a three-month monitoring period. The REE patterns obtained showed the presence of Gadolinium (Gd) anomalies in the dissolved and total fractions as well as in *Corbicula fluminea*. The apparent bioavailability of natural REEs was in the following order for the dissolved fraction: Medium REEs (MREEs) > Light REEs (LREEs) > Heavy REEs (HREEs) and for the particulate fraction: MREEs > LREEs = HREEs. These results highlight the importance of the particulate fraction in the study of the bioavailability of REEs in bivalves. An increase of anthropogenic Gd (Gd<sub>anth</sub>) was observed in the dissolved fraction between the upstream site (3.4 ng.L<sup>-1</sup>) and the WWTP Downstream site (48.4 ng.L<sup>-1</sup>). The Gd anomaly observed in the water was also observed in *Corbicula fluminea* with a significant increase in the bioaccumulation of Gd<sub>anth</sub>, from 1.5±1 ng.g<sub>DW</sub><sup>-1</sup> upstream to 4.1±0.7 ng.g<sub>DW</sub><sup>-1</sup> downstream of the WWTP effluents, thus confirming the enhanced bioavailability of medical-origin Gd to freshwater bivalves. This study strongly suggests that *Corbicula fluminea* can be used as a sentinel species in the monitoring of Gd contamination of medical origin. It would thus appear important to consider the potential entry of this contaminant into the human food chain *via* other, commercially exploited bivalve species.

Keywords: REEs, Gadolinium anomaly, Asian clam, bivalves, bioavailability, urban river
## 1. Introduction

Continental waters are subject to considerable anthropogenic pressure, particularly with the release of many contaminants of anthropogenic origin (e.g. agricultural, industrial, urban), such as trace metals (e.g. cadmium, zinc, lead), seriously modifying the natural geochemical cycles of metals (e.g. Meybeck et al., 2007; Nriagu, 1988; Reza and Singh, 2010; Viers et al., 2009) and impacting the ecosystems (e.g. Bocchetti et al., 2008; Lanceleur et al., 2011; Rainbow, 2007; Rashed, 2001). The increase in the global population, and in the ongoing growth of urban centers, is leading to an intensification in urban wastewaters release (e.g. effluents of domestic, industrial and hospital wastewater, rainwater runoff) into hydrosystems (e.g. Deycard et al., 2014; Eriksson et al., 2007; Feng et al., 2004; Gundacker, 2000). At the same time, over the last 20 years, the development of new technologies, associated with a desire to reduce the consumption of fossil resources, has led to the demand, use and release of new metallic elements, considered as emerging contaminants, including the Rare Earth Elements (REEs) which are used in many modern technologies (e.g. green energy, automobiles, healthcare, agriculture). This group of elements includes the whole lanthanide series (15 elements), as well as scandium and yttrium.

Lanthanide series are commonly divided into three groups following their atomic weight (e.g. Bru et al., 2015; Kogel et al., 2006): i) the light REEs (LREEs – La, Ce, Pr and Nd); ii) the medium REEs (MREEs – Sm, Eu and Gd); and iii) the heavy REEs (HREEs – Tb, Dy, Ho, Er, Tm, Yb and Lu). Several studies reported the geochemical characterization of waters and sediments in REEs (e.g. Delgado et al., 2012; Elbaz-Poulichet et al., 2002; Gwenzi et al., 2018; Ma et al., 2019).

Some of the REEs are relatively well documented (e.g. lanthanum, cerium, samarium, gadolinium) due to their increased presence in aquatic systems subject to anthropogenic pressure (e.g. Lerat-Hardy et al., 2019; Klaver et al., 2014; Kulaksız and Bau, 2013; Qing and Feng, 2016).

However, for the most part, the sources of these emerging elements are still poorly defined.

Similarly, current knowledge of the ecotoxicological effects of REEs remains fragmentary (e.g. Freitas et al., 2019; Hanana et al., 2017; Lortholarie et al., 2019; Parant et al., 2019). Recent work
described the impacts of REEs on aquatic ecosystems, focusing particularly on their bioavailability and effects at different trophic organization levels, both in laboratory experiments (e.g. Blinova et al., 2018; Fuma et al., 2001; González et al., 2015; Weltje et al., 2002) and directly in natural habitat (e.g. Li et al., 2016; Mayfield and Fairbrother, 2015; Romero-Freire et al., 2018). For example, Weltje et al. (2002) studied the distribution of REEs in several compartments (e.g. aquatic plants, mollusks, sediments, waters) and were able to show, for the plant *Potamogeton pectinatus*, that the interstitial water in sediments is a major source of REEs accumulation. These authors also observed that REEs partition between the soft tissue and the shells of mollusks (*Potamopyrgus antipodarum*, *Lymnaea stagnalis*, *Radix ovata*, *Physella acuta*, *Planorbis planorbis*, *Planorbis corneus*, *Corbicula fluminea* and *Dreissena polymorpha*). Despite the increase in REEs concentrations observed in aquatic systems subject to urban pressure, very few studies have used the technique of transplanting species in order to monitor such contaminations (Perrat et al., 2017). The species transplantation monitoring that has been carried out has mainly been used to monitor both short- and long-term changes in contamination by classic, "regulated" metals in aquatic systems (e.g. Besse et al., 2013; Cazenave et al., 2014; Gold et al., 2002; Reynders et al., 2008). Among the bioindicator sentinel species exposed in cages *in situ*, filtering bivalves, and in particular the Asian clam *Corbicula fluminea*, are regularly used (e.g. Andrès et al., 1999; Arini et al., 2014a; Gunther et al., 1999; Marie et al., 2006; Peltier et al., 2009; Roméo et al., 2003). This sentinel species is widely used because both its physiology and its responses to disruption are well known (e.g. Achard-Joris et al., 2006; Arini et al., 2014b; Baudrimont et al., 2003, 1997; Ren et al., 2013; Sousa et al., 2008). Furthermore, its transcriptome has been entirely sequenced, thus favoring environmental studies using this biological model (Bertucci et al., 2018).

Compared to heavy metals, current knowledge is weak concerning the environmental impact of anthropogenic REEs. Therefore, it is urgent to extensively investigate their risk to environment by studying the levels and patterns of REEs in geochemical and biological compartments. In this
context, the objectives of this study are to: i) characterize REE concentrations and anomalies in the water of an urban river submitted to intense anthropogenic pressure, ii) determine how natural and anthropogenic REEs are partitioned in the water, iii) monitor the bioaccumulation of natural REEs in *Corbicula fluminea* and iv) evaluate the bioavailability of anthropogenic REEs in *Corbicula fluminea*. The final objective is to better understand the mechanisms of REEs uptake by this species as a function of the REEs partitioning between the dissolved and the particulate phases and to verify whether it is possible to use this biological model as a sentinel species for REEs contamination of urban origin. Therefore, this study aims to proposed in situ biological and geochemical data for future risk assessment of anthropogenic REEs in urban areas.

## 2. Materials & Methods

### 2.1. Presentation of the study site and experimental setup

The study focuses on one type of urban waste, the effluents from wastewater treatment plants (WWTP), which contributes significantly to the contamination of aquatic systems by combining different sources (e.g. domestic, industrial and hospital wastewater). The study site is the Jalle River, an urban freshwater stream that drains Bordeaux Metropole, France's seventh biggest urban agglomeration, which is currently undergoing rapid expansion. The Jalle River is a tributary of the Garonne River which, further downstream, becomes the Gironde Estuary after its confluence with the Dordogne River. The Jalle River is 32 km long and drains a watershed of 330 km² with an annual average discharge of 1.80 m³.s⁻¹. Water discharges data and physicochemical analyses were provided by Lyre laboratory of Suez. The watershed of the Jalle River covers seven municipalities with 110,000 inhabitants. The principal land-uses in the watershed are market gardening, cattle-rearing and forestry in an area that is mainly covered by forest upstream and very urbanized elsewhere. Downstream, the river receives the effluents from a major wastewater treatment plant with a treatment capacity of 85,000 population equivalents and an average discharge of 0.19 m³.s⁻¹ during the study period. The ecological state of the water body was classified as "medium" in 2016 based on the European Water Framework Directive criteria.
For this study, two sites were monitored on the Jalle River (Figure 1). The Thil site, upstream of the WWTP effluents, acted as a control site for the water quality and for *in situ* bioaccumulation in bivalves. The WWTP Downstream site, located downstream of the WWTP effluents, made it possible to determine the impacts of the WWTP on the geochemical quality of the water and on REEs accumulation in *Corbicula fluminea*. The Jalle River separates into two distinct arms between the Thil and WWTP Downstream sites. The latter, as well as the WWTP effluents, are located on the southern arm of the Jalle River (Figure 1). The water coming directly from the WWTP effluents was also monitored during this study. The population of *Corbicula fluminea* used during this study came from the Isle River and were taken from the experimental station of INRAE at Saint-Seurin-sur-l'Isle, before a period of two weeks acclimation in the laboratory (Bertucci et al., 2018). During acclimation, bivalves were maintained in open circuit tanks and feed with microalgae (*Scenedesmus* sp.). Bivalves (*Corbicula fluminea*) were installed in cages (for more details see Bertucci et al., 2018), on the riverbed, for three months upstream and downstream of the WWTP effluent, in parallel with monitoring of geochemical water quality. During the 85 days of caging, no mortality was observed at the Thil site and 6% of mortality was observed at the WWTP Downstream site.

## 2.2. Sampling, treatment and analysis

Monitoring took place over a three-month period between March and June 2016. Water samples were taken on three contrasting hydrologic conditions: i) at the end of a period of high water in March, ii) during intermediate water discharges in April and iii) at the beginning of a period of low water in June. Water from the WWTP effluents was sampled during complementary campaigns between July 2016 and January 2018 (n=5). At each sampling time and at each site, samples were divided in two fractions (500mL per fraction). A filtered dissolved phase (Sartorius-S Minisart®, porosity <0.2µm), acidified using ultra-pure HNO₃ (J.T. Baker®, 15M) and an unfiltered total phase treated with ultra-pure HNO₃ (J.T. Baker®, 15M), ultra-pure HCl (J.T. Baker®, 11M) and H₂O₂ (J.T. Baker®, 30-32%). Samples of water from the WWTP effluents were
filtered and prepared only for the dissolved phase, using the same protocol as for the water samples from the Jalle River. All the samples were stored in polypropylene bottles previously decontaminated using HNO₃ (Lerat-Hardy et al., 2019) and kept in the dark at 4°C pending analysis.

Before the *in-situ* transplantation of *Corbicula fluminea* into the monitored sites, a batch of five organisms from the population at Saint-Seurin-sur-l'Isle was separated and conserved in order to obtain the initial condition index (CI) of the population (Equation 1). This index, expressed as a percentage, is the ratio between the dry weight of the whole organism (DWwo) and the dry weight of the shell (DWShell). Previous study of Arini et al. (2014a) used CI to provide information about the state of health of the individuals. The bivalves were then placed in cages *in situ* at each site (Thil and WWTP Downstream) in batches of 15 individuals for the 85 days of the study (March to June). After the monitoring period, all the individuals were then recovered and stored in the laboratory at -80°C before being treated and analyzed. The soft tissues of five individuals from each site were freeze-dried, weighed and then digested with Aqua Regia (1.4mL ultra-pure HNO₃; J.T. Baker®, 15M; and 2mL ultra-pure HCl; J.T. Baker®, 11M) for 3h at 100°C on a hot plate (Mikolaczyk et al., 2016).

$$CI (\%) = \frac{DW_{wo}}{DW_{Shell}} \times 100 \qquad (1)$$

REE concentrations were determined for all the biological and inorganic samples using a direct method (5mL per sample) with a Triple Quadrupole Inductively Coupled Plasma Mass Spectrometer (Thermo Scientific® iCAP TQ – ICP-MS). The TQ-O₂ analytical method was used in order to eliminate some of the interference and single-element solutions were analyzed with the samples in order to calculate and correct interferences that had not been eliminated (Lerat-Hardy et al., 2019). The method used to calculate interferences is identical to that described by Lerat-Hardy et al. (2019) and the detection limits for the analyzed samples ranged between 0.05 ng.L⁻¹ for Tb and 1.23 ng.L⁻¹ for Ce (supplementary data). In the WWTP effluent samples, the
154 correction percentages obtained for Eu were too high for reliable correction and, thus no Eu
155 concentrations are shown for these samples. In order to assess the accuracy and precision of the
156 measurements, a certified reference water was analyzed (SLRS-6; Table 1; Yeghicheyan et al.,
157 2019). Yeghicheyan et al. (2019) characterized REE concentrations in SLRS-6 by an
158 interlaboratory comparison (n=9) and authors considered their values as robust concentrations
159 (120 to 135 analyses per element) for a routinely use in laboratories. Results showed mean
160 recoveries of 91% with mean precision < 9% (RSD) for all REEs (supplementary data). In the
161 Jalle River waters and the WWTP effluent samples, the Sm concentrations are estimated and
162 obtained with a polynomial regression method.

163 **2.3. Data treatment**

164 Correlation coefficients (r) were calculated to estimate the relation between: i) water discharges
165 and REE concentrations of the dissolved, total and particulate phases; and ii) both groups of
166 *Corbicula fluminea* exposed at the Thil and the WWTP Downstream sites. Correlation
167 coefficients were calculated with Excel®. According to Taylor (1990),"high" correlations were
168 considered for r>0.68 and "very high" correlations for r>0.90. The significance of the correlations
169 was statistically tested within R® (α = 0.05).

170 Two major mathematical methods exist for the calculation of REE anomalies from the REE
171 patterns. The first is a linear method with the interpolation of the anomaly from the shale-
172 normalized neighboring REEs (e.g. Elbaz-Poulichet et al., 2002; Hatje et al., 2016; Klaver et al.,
173 2014). The second method is a logarithmic modeling when Ce shows high negative anomaly in
174 normalized patterns (e.g. Kulaksız and Bau, 2013, 2011; Merschel et al., 2015). In this study,
175 preference was given to a polynomial regression method (Equation 2 & 3) in order to have a
176 unique method of anomaly calculations for biological and geochemical samples. Models were
177 performed using Excel® and coefficients of determination (R²) were calculated to determine the
178 reliability of models for each sample. We considered that R² values higher than 0.90 obtained
179 between calculated and measured concentrations have high reliability.
$$ [REEi] = REEi_{norm} * EUS_{REEi} \qquad (2) $$

$$ REEi_{norm} = C_n * P_{REEi}^n + C_{(n-1)} * P_{REEi}^{(n-1)} + \dots + C_1 * P_{REEi} + C_0 \qquad (3) $$

In equation 2: *REEi* is the chosen REE; [*REEi*] is the calculated concentration of *REEi*; *EUS*<sub>REEi</sub> is the corresponding concentration of *REEi* in the EUS reference material (Bau et al., 2018); *REEi*<sub>norm</sub> is the EUS-normalized concentration of *REEi*. In equation 3: *n* is the degree of each polynomial; *C*<sub>*n*</sub> is the constant of each polynomial; *C*<sub>0</sub> is the y-intercept; *P*<sub>REEi</sub> is the position of *REEi* in the lanthanide series (ex. *P*<sub>Gd</sub> = 7). These calculations provided the natural concentrations of REEs and, by difference with the measured concentrations, the anthropogenic concentrations.

Statistical comparisons were performed on: i) condition index between the reference and the Jalle River organisms; and ii) bioaccumulated REE concentrations in *Corbicula fluminea* between both caging stations in the Jalle River. Non-parametric tests (Kruskal-Wallis) were used with an alpha risk of 5% within R®.

## 3. Results

### 3.1. Change in water discharges and physical chemistry of the water

In 2016, the water discharges of the Jalle River varied between 0.45 and 51 m³.s⁻¹ at the Thil site and between 0.37 and 44 m³.s⁻¹ at WWTP Downstream site. During the caging campaign from March to June, the measured water discharges varied by a factor of 9, from 0.71 to 6.46 m³.s⁻¹ at the Thil site and from 0.66 to 5.78 m³.s⁻¹ at the WWTP Downstream site (Table 2). The beginning of this period was marked by somewhat high discharge at the end of a flood episode, whereas the end of the monitoring period was representative of low discharge conditions. From the daily water discharges (Q<sub>d</sub>) covering the 85 days of caging, we established that 11% of the study period could be associated with flood and/or high flow conditions (Q<sub>d</sub> > 2.5 m³.s⁻¹), 49% with average flow rates (2.5 m³.s⁻¹ > Q<sub>d</sub> > 1.5 m³.s⁻¹) and 40% with low discharge (Q<sub>d</sub> < 1.5 m³.s⁻¹). The physicochemical parameters from the two sites were monitored between July 2013 and September
205 2018 during complementary campaigns (n=12). Significant increases were observed in several
206 parameters between Thil and WWTP Downstream including: BOD5 (2.3-7.6 mgO2.L-1), Chemical
207 Oxygen Demand (COD; 16.8-33.3 mgO2.L-1), Dissolved Organic Carbon (DOC; 4.9-7.3 mg.L-1),
208 NO3 (4.5-18.1 mg.L-1), NH4+ (0.3-1.4 mg.L-1) and NO2 (0.1-1.8 mg.L-1).

209 **3.2. REE concentrations in surface waters**

210 The REE concentrations obtained for the dissolved and total fractions are summarized in Table 2.
211 The difference between the total and dissolved fractions provides an indirect estimate of the
212 particulate fraction, also shown in Table 2. The REE concentrations include several noteworthy
213 results: First, the concentrations obtained at Thil are mainly higher than those obtained at WWTP
214 Downstream on the same date, whatever the fraction. Second, the contribution of the dissolved
215 fraction to the total fraction shows a generally increasing trend as one moves towards the heavier
216 REEs (HREEs) from 30% for La to 60% for Lu at Thil in June 2016 and from 31% for La to
217 nearly 99% for Lu at WWTP Downstream in April 2016 (Table 2). Only Ce and Yb show a
218 slightly different pattern with the contribution of the dissolved fraction lower than the general
219 trend for Thil during all three campaigns and for WWTP Downstream in March and April,
220 whereas the contribution of dissolved Gd is higher at WWTP Downstream for the April and
221 June campaigns. Third, a decrease over time occurred for both sites and for all fractions, with
222 higher concentrations during high water discharge (March) and lower values at low discharge
223 (June), except for Gd showing the highest dissolved and total concentrations in April at WWTP
224 Downstream (Table 2). In fact, the concentrations of dissolved REEs (except Gd) increase by 50%
225 for all the elements at the Thil site and by between 55% (Yb, Lu) and 70% (La, Pr, Eu) at the
226 WWTP Downstream site during the flood. The concentrations of dissolved REEs show significant
227 positive correlations with water discharges for the majority of REEs (r>0.95; p-value<0.01),
228 except Gd (r=0.08). The total and particulate concentrations of REEs are also higher during flood
229 situation (by 20% to 70%) showing significant positive correlation between the total fraction and
230 water discharges (r>0.85; p-value<0.03 except for Gd with r=0.56). For the particulate fraction,
correlations with discharge ranged from r=0.40 for Lu to r=0.79 for Ce, Nd and Dy. Finally, the dissolved REEs fraction of the water from the WWTP effluent shows, on average, lower concentrations than those obtained in the Jalle River decreasing from 95% (La, Pr, Nd) to 65% (Yb and Lu), yet unlike Gd showing very high concentrations (326 ± 125 ng.L⁻¹), noticeably higher than those found in the Jalle River (Table 2).

The natural abundance of REEs differs depending on whether the element has an odd or even atomic number. In order to mask these variations, it is standard practice to normalize sample concentrations with those from reference geological materials. European Shale (EUS; Bau et al., 2018) was used as a normalizer in order to smooth out the natural variations in concentrations of REEs in the environment. This material was chosen as being representative of the study area. The EUS-normalized dissolved, total and particulate REEs concentrations in the Jalle River are shown in Figure 2. The patterns obtained for the dissolved fraction (Figure 2A) show an increase in the [REE]/[EUS] ratio from light REEs (LREEs) to HREEs. These patterns show a small negative anomaly in Ce for all the profiles, a light positive anomaly in Eu in periods of high water (March) and a positive anomaly in Gd at the WWTP Downstream site in April and June. The overall pattern in the total fraction (Figure 2B) shows a trend similar to that of the dissolved fraction with an increase from LREEs to HREEs. However, in the total fraction an increase in the [REE]/[EUS] ratio of LREEs to MREEs occurs towards a maximum for Eu, followed by a decrease between Eu and Tb, except for WWTP Downstream site on April and June and for Thil site on June. The overall REE patterns in the particulate fraction tend to show a slight increase from LREEs to medium REEs (MREEs) with a maximum for Eu, then a slight decrease from MREEs to HREEs (Figure 2C). A large positive Gd anomaly in the total fraction occurs at the WWTP Downstream site (April) and to a lesser extent in June. Finally, the general pattern of the dissolved concentrations in the water from the WWTP effluents (Figure 2A) shows a large positive Gd anomaly at any time, and was attributed to anthropogenic Gd (Gd<sub>anth</sub>).
The concentrations of Gd<sub>anth</sub> were calculated from the difference between the measured concentration of Gd and the calculated natural value for Gd (Gd<sub>nat</sub>) obtained by modeling. The coefficients of determination obtained for the polynomial regression models of each sample (mean; min/max) were: 0.98; 0.97/0.99 for the dissolved fraction and 0.97; 0.93/0.99 for the total fraction. The Gd<sub>anth</sub> concentrations obtained for the particulate fraction were calculated from the difference between the total and dissolved fractions. The calculated Gd<sub>anth</sub> concentrations show a maximum of 86.6 ng.L<sup>-1</sup> and 86.9 ng.L<sup>-1</sup> respectively for the dissolved and total fractions at WWTP Downstream (June). The mean concentrations of Gd<sub>anth</sub> and Gd<sub>nat</sub> as determined for the WWTP effluents are 324 ± 126 ng.L<sup>-1</sup> and 2.0 ± 1.3 ng.L<sup>-1</sup> respectively (Table 2).

A unique profile was established for each fraction and station by assuming that the REE patterns observed in March, April and June are respectively representative of flood/high water discharges, average water discharges and low water discharge. During the caging period, we have established that 11%, 49% and 40% of the 85 days of study period are respectively associated with flood/high, average and low water discharges. These patterns (Figure 2D) could then be compared with the bioaccumulation results.

## 3.3. Bioaccumulation of REEs in *Corbicula fluminea*

The individuals caged in the Jalle River show a significant increase in mean condition index (CI ± SE) compared to the reference population taken from the Isle River before caging (CI=3.0±0.2).

The values obtained for Thil (6.3±0.4) and WWTP Downstream (7.0±0.4) are not significantly different (Kruskal-Wallis test), suggesting that REE concentrations (mean ± SE) bioaccumulated by bivalves (n=5) at each site are comparable between the batches of individuals caged in the Jalle River (Table 2).

The average concentrations of bioaccumulated REEs in organisms (n=5) are EUS-normalized and presented as REE patterns (Figure 3A). The data show inverse V-shaped profiles with an overall increase from LREEs to MREEs and then a decrease from MREEs to HREEs. Maximum values
occur for Eu, Gd and minimum values for La, Ce, Yb and Lu. The REE patterns obtained for Thil and WWTP Downstream are, proportionally, very similar, with a correlation coefficient of r=0.98 between the two sites, except for Gd which does not follow the same trend, thus seeming to indicate the influence of Gd<sub>anth</sub> (Figure 3A).

The concentrations of Gd<sub>anth</sub> and Gd<sub>nat</sub> (Table 2) were calculated using the same method as that described earlier. One polynomial regression model was produced per organism and the results show R<sup>2</sup> (mean; min/max) of: 0.88; 0.87/0.91 at Thil and 0.91; 0.87/0.94 at WWTP Downstream.

The concentrations of Gd<sub>anth</sub> are 1.5±1 ng.g<sub>DW</sub><sup>-1</sup> for Thil and 4.1±0.7 ng.g<sub>DW</sub><sup>-1</sup> for WWTP Downstream compared with 109±19 and 45±4 ng.g<sub>DW</sub><sup>-1</sup> for Gd<sub>nat</sub>, respectively. The REE concentrations in the individuals caged in the Jalle River are lower by ~58% between Thil and WWTP Downstream with a maximum difference of 61% for Eu and a minimum of 56% for Gd and Lu. The mean concentrations of the individuals from the WWTP Downstream site were normalized with respect to those from the Thil site (Figure 3B). This profile shows a mean ratio of 0.42, expressing the 58% reduction observed between the two batches of organisms. Moreover, three anomalies may be observed, a negative anomaly for Eu (0.39) and two positive anomalies, one for Gd (0.44) and the other for Lu (0.44; Figure 3B).

The bioconcentration factors (BCF) were calculated from the ratio between the mean concentration of bioaccumulated REEs and the mean concentration of the water discharge-weighted total fraction, for the two sites (Figure 4A). None REE show anthropogenic anomaly, except Gd, on the REEs patterns. Therefore, all REEs concentrations are considered natural, with the exception of Gd. Because of the presence of anthropogenic Gd, the Gd natural BCFs were calculated from the previously determined concentrations of Gd<sub>nat</sub> (Table 2) and the Gd overall BCFs were calculated with Gd concentrations (Gd<sub>nat</sub> + Gd<sub>anth</sub>). The profiles obtained for the natural and overall (natural + anthropogenic) BCFs are bell-shaped with an increase from LREEs to MREEs and a reduction from MREEs to HREEs. The maximum values are obtained for Eu at the Thil site (BCF=1,600) and for Gd at the WWTP Downstream site (BCF=1,020), whereas
minimum values are obtained for Yb at the Thil site (BCF=630) and at the WWTP Downstream site (BCF=350). A reduction in the BCF of Eu is observed between Thil and WWTP Downstream sites. For the overall profiles (Figure 4A), a decrease of BCF appears for Gd at the WWTP Downstream site (BCF=520). The distribution coefficients (D<sub>REE</sub>) were also calculated between the mean bioaccumulation in *Corbicula fluminea* and the different fractions of water studied (dissolved; particulate). The following equation (Equation 4) was used, as previously applied by Merschel and Bau (2015) for REEs bioaccumulation in *Corbicula fluminea* shells.

$$D_{REE} = \frac{[REE]_{C.fluminea}}{[REE]_{water}} \quad (4)$$

The D<sub>REE</sub> was calculated for Thil and WWTP Downstream using the mean bioaccumulation values and the average of water-discharge weighted concentrations for the dissolved and particulate fractions (Table 2). As for the BCF, all REEs concentrations are considered natural, except for Gd. Therefore, the concentrations of Gd<sub>nat</sub> were used to calculate the natural dissolved Gd D<sub>REE</sub> and the overall dissolved Gd D<sub>REE</sub> was calculated as the sum of Gd<sub>nat</sub> and Gd<sub>anth</sub> (Figure 4B). These dissolved D<sub>REE</sub> profiles show a slight increase from LREEs to MREEs and a strong decrease from MREEs to HREEs. A maximum is observed for Eu at the Thil (D<sub>REE</sub>=4,460) and WWTP Downstream (D<sub>REE</sub>=2,360) sites and a minimum for Lu with D<sub>REE</sub>=1,100 and D<sub>REE</sub>=520 for Thil and WWTP Downstream, respectively. A small positive anomaly in Ce may be observed on these profiles with D<sub>REE</sub>=3,500 for Thil and D<sub>REE</sub>=2,180 for WWTP Downstream. For the overall (natural + anthropogenic) D<sub>REEs</sub> a small negative anomaly may be observed in Gd at the Thil site (D<sub>REE</sub>=3,730) and a strong negative anomaly in Gd for the WWTP Downstream site (D<sub>REE</sub>=720). For the particulate D<sub>REE</sub>, the natural and overall profiles are similar and do not show any anomaly. The particulate D<sub>REE</sub> obtained have a bell-shaped profile with a maximum for MREEs (Eu, Gd) and minimum D<sub>REE</sub> for LREEs and HREEs. A reduction in the D<sub>REE</sub> of Eu may be observed between the Thil and WWTP Downstream sites. The maximum D<sub>REE</sub> are obtained for Eu (D<sub>REE</sub>=2,530) at the Thil site and for Gd (D<sub>REE</sub>=1,890) at the WWTP Downstream site
whereas the minima are found for Ce and Yb at both sites with D<sub>REE</sub>=1,260, D<sub>REE</sub>=1,270 respectively for the Thil site and D<sub>REE</sub>=900, D<sub>REE</sub>=850 for the WWTP Downstream site.

## 4. Discussion

### 4.1. Assessment of geochemical water quality

This study has focused on the impact of domestic wastewaters through WWTPs, considered to be one of the main pathways by which urban contaminants enter the natural environment. The patterns obtained for the three fractions (Figure 2) are consistent with other studies (e.g. Akagi and Edanami, 2017; Bau et al., 2018; Lerat-Hardy et al., 2019; Schmidt et al., 2019). All the REEs, with the exception of Gd, showed their highest concentrations at high water discharges and at the Thil site, although the WWTP drains the areas hosting the main anthropogenic sources. Accordingly, high REEs values in the upstream Jalle River during periods of rainfall would be mostly of natural origin, as a result of leaching and mechanical erosion of podzols located upstream (Migaszewski and Gałuszka, 2015). At low discharge, the Jalle River receives a greater proportion of its water from the water table and/or tributaries draining the downstream part of the watershed where pedology (soils developed on clays deposited by the Garonne River during the Flandrian period) is different from that in the upstream watershed (podzol; Gis Sol, 2011). Dissolved and total REEs concentrations show significant positive correlations with water discharges and only Gd showed weak correlation. However, dissolved Gd<sub>nat</sub> is strongly dependent on water discharges (r=0.95) unlike Gd<sub>anth</sub> (r=-0.28). This shift can be explained by the high Gd concentrations at the WWTP Downstream site due to high dissolved Gd concentrations entering into the hydrosystem by the WWTP effluents. This anthropogenic Gd impact its natural partitioning and cycle. Several studies have shown anomalies in Gd in rivers (e.g. Bau and Dulski, 1996; Elbaz-Poulichet et al., 2002; Hatje et al., 2016) because of its use as a paramagnetic contrast agent for medical magnetic resonance imaging (MRI), particularly in hospital wastewater (e.g. Kümmerer and Helmers, 2000; Künnemeyer et al., 2009; Lerat-Hardy et al., 2019). Gd<sub>anth</sub> is thus a very good marker for this type of wastewater (Möller et al., 2000). Due to their particular
chemical speciation, Gd-based contrast agents are extremely stable in their dissolved form and are thus not removed by WWTPs (Möller et al., 2002). In the Jalle River, very low $Gd_{anth}$ concentrations at the Thil site may derive from urban wastewater treated in a small WWTP 14km upstream (25,000 pop-eq.). However, Gd anomalies are mainly present downstream of the studied WWTP effluents and the dissolved/total ratios show that 79% of the Gd is in dissolved form at the WWTP Downstream site compared to a mean of 39% at the Thil site. Moreover, the quantification of $Gd_{anth}$ in the sampled water fractions suggests that, on average, 97% of this $Gd_{anth}$ is in a dissolved form at the WWTP Downstream site. All of these observations confirm the idea that dissolved $Gd_{anth}$ is being introduced into the natural environment *via* the WWTP, with a relatively high contribution to dissolved Gd load during low to moderate water discharge, when dilution by other surface waters is low.

## 4.2. Bioavailability of natural Rare Earth Elements

The bioavailability of natural REEs was studied by the measure of their bioaccumulation in the soft tissues of *Corbicula fluminea* in order to provide an initial approach on this model species widely used in aquatic ecotoxicology. The normalization of the bioaccumulation of individuals from the WWTP Downstream site with those from Thil (Figure 3B) showed a mean ratio of 0.42 indicating lower bioaccumulation by 58% for the majority of the REEs in the WWTP Downstream site, which reflected the concentrations in the water.

Given the preferential assimilation of the particulate fraction of REEs in benthic bivalves (e.g. Akagi and Edanami, 2017; Wang et al., 2019) it is possible that the lower particulate REEs levels at the WWTP Downstream site explain the lower bioaccumulation observed in *Corbicula fluminea* at this site. Moreover, the minimum ratio WWTP Downstream/Thil for Eu (Figure 3B) could be due to different factors including: i) the presence of a lock between the two monitoring sites, thus implying potential modifications to the hydrodynamics and particles (and associated REEs) trapping; and ii) variations in physicochemical parameters due to the mixing of water from the Jalle River with that from the WWTP effluents. These factors might imply local modifications
384 in the physicochemical parameters (e.g. dissolved organic matter, pH and temperature) and thus,
385 modifications in the REEs speciation at the WWTP downstream site. Indeed, previous studies
386 have shown that the speciation of Eu is particularly sensitive to such physicochemical variations
387 in the environment (e.g. Kulaksız and Bau, 2013; Leleyter et al., 1999; Sverjensky, 1984).
388 Therefore, the speciation of Eu may have changed between the Thil and the WWTP Downstream
389 sites with the local modifications of physicochemical parameters rendering Eu less bioavailable
390 for *Corbicula fluminea* at the WWTP Downstream site. However, more information is need on
391 the Eu concentrations in the WWTP effluents and sediment and Eu reactivity to verify or reject
392 this hypothesis. A potential competition between Eu and another element could be considered as
393 previously highlighted by Qing and Feng (2016) between Ce and Cd in the pacific oyster
394 *Crassostrea gigas*.

395 The bioavailability of natural REEs in *Corbicula fluminea* was studied by using the calculated
396 natural concentrations for Gd (Gd<sub>nat</sub>) for BCF patterns (Figure 4A). These patterns also show an
397 inverse V-shaped distribution (bell-shaped profiles) reflecting greater bioavailability of natural
398 MREEs in *Corbicula fluminea* with a maximum for Eu and Gd, suggesting the following order of
399 bioavailability for the total fraction of the natural REEs: MREEs > LREEs > HREEs. The order
400 of bioavailability of natural REEs in different fractions was estimated from the distribution
401 coefficients of the REEs (D<sub>REE</sub>), i.e. the ratio between the mean bioaccumulation in *Corbicula
402 fluminea* and the dissolved and particulate fractions (Equation 4). As for the BCF, the
403 concentrations of Gd<sub>nat</sub> were used to calculate the natural dissolved (Figure 4B) and particulate
404 D<sub>REEs</sub> (Figure 4C). The obtained D<sub>REE</sub> profiles for the dissolved fraction (&lt;0.2µm) show a slight
405 increase from LREEs to MREEs and then a strong decrease from MREEs to HREEs with a
406 maximum for Sm, Eu and Gd<sub>nat</sub>. These patterns would appear to indicate preferential assimilation
407 of MREEs from the dissolved fraction and enable the following order of bioavailability to be
408 determined: MREEs > LREEs > HREEs. In contrast, dissolved D<sub>REE</sub> (&lt;0.2µm) reported by
409 Merschel and Bau (2015) on *Corbicula fluminea* shells from the Rhine River showed an overall
410 decrease in dissolved D<sub>REE</sub> from LREEs to HREEs with a small positive anomaly in Ce. The
411 difference observed in terms of MREEs between the soft tissue (this study) and that of Merschel
412 and Bau (2015) on *Corbicula fluminea* shells, may suggest that there is fractioning of the REEs
413 between their assimilation by direct and trophic pathways and their transfer into the shell *via* the
414 extra-palleal fluid. However, one cannot exclude that this observed difference results from a
415 difference in the geochemical background as well as in the composition and/or the speciation of
416 REEs between the two rivers. The D<sub>REE</sub> calculated for the dissolved fraction also shows a small
417 positive anomaly in Ce (similar to that reported by Merschel and Bau, 2015) reflecting preferential
418 assimilation of dissolved Ce compared to the other LREEs (La, Pr, Nd).

419 Akagi and Edanami (2017) showed that the REE patterns for the soft tissue of benthic bivalves
420 and those for suspended particulate matter and sediments had inverse V-shaped profiles, with a
421 maximum for MREEs (Eu, Gd). The REE patterns for the soft tissue of *Corbicula fluminea* also
422 show inverse V-shaped profiles with a maximum for Eu and Gd (Figure 3A) and the particulate
423 fraction show slight bell-shaped REE patterns (Figure 2C). Moreover, Bonnail et al. (2017)
424 obtained similar REE bioaccumulation patterns for the soft tissues of *Corbicula fluminea*, after
425 exposure to contaminated sediments from Acid Mine Drainage. The particulate fraction seems to
426 be an important fraction of REEs bioaccumulation in *Corbicula fluminea*. The profiles of natural
427 particulate D<sub>REEs</sub> (Figure 4C) show a bell-shaped profile supporting maximum bioavailability for
428 MREEs (Sm to Ho) with the following order of bioavailability: MREEs > LREEs = HREEs. The
429 positive anomaly observed for Gd will be discussed in the following paragraph. The comparison
430 of dissolved and particulate D<sub>REE</sub> seems to indicate that LREEs and MREEs (La to Dy) are
431 preferentially assimilated from the dissolved fraction and that HREEs (Ho to Lu) are preferentially
432 assimilated from the particulate fraction. The results obtained for particulate D<sub>REE</sub> show that the
433 latter fraction is non-negligible in the evaluation of the bioavailability of REEs, particularly for
434 species at the water-sediment interface (e.g. Akagi and Edanami, 2017; Mayfield and Fairbrother,
435 2015; Wang et al., 2019) such as *Corbicula fluminea*.
436 **4.3. Bioavailability of anthropogenic Gd**

437 Gadolinium shows major anomalies in the Jalle River with a possible effect on the organisms.

438 Recent studies have investigated the toxicological impact of Gd-based contrast agents and have

439 shown a certain number of harmful effects in humans, particularly bioaccumulation of the element

440 in the human brain (e.g. Grobner, 2006; Kanda et al., 2015; Sanyal et al., 2011). These

441 observations may indicate potential bioaccumulation of Gd<sub>anth</sub> in freshwater species present

442 downstream of the WWTP outfall.

443 For the caged organisms in the Jalle River, an anomaly in bioaccumulation of Gd was also

444 determined in *Corbicula fluminea* (Figures 3A and 3B). Calculation of the [Gd<sub>anth</sub>]/[Gd] ratio

445 shows significantly higher (Kruskal-Wallis test) percentages of Gd<sub>anth</sub> in organisms at the WWTP

446 Downstream site (8.7%) than at the Thil site (1.4%), suggesting that the Gd<sub>anth</sub> contained in the

447 WWTP effluents is bioavailable to *Corbicula fluminea*. The BCFs patterns for the overall

448 concentrations (natural + anthropogenic; Figure 4A) show a negative Gd anomaly at the WWTP

449 Downstream site, which could indicate inhibited uptake or excretion of Gd at this site. The

450 comparison, for this site, of the BCFs of natural (BCF=1,120) and anthropogenic (BCF=83) Gd

451 thus seems to indicate that Gd<sub>anth</sub> is less bioavailable than Gd<sub>nat</sub>. Previous laboratory studies on

452 the bioavailability of medical-origin Gd indicated that Gd<sub>anth</sub> is bioavailable to organisms under

453 exposure concentrations much greater than environmentally relevant levels (e.g. Braun et al.,

454 2018; Hanana et al., 2017; Lingott et al., 2016; Perrat et al., 2017). The Gd<sub>anth</sub> measured at the

455 WWTP Downstream site is mainly in dissolved form (97%), whereas particulate natural REEs

456 seem to be a major source of assimilation of REEs in benthic bivalves such as *Corbicula fluminea*.

457 Moreover, Lingott et al. (2016) have shown that the bioaccumulation of medical-origin Gd is due

458 to a concentration-dependent diffusion process. These results could therefore explain the weak

459 assimilation of Gd<sub>anth</sub> in benthic species that are less dependent on the dissolved fraction of REEs.

460 Furthermore, Perrat et al. (2017) have shown that defense mechanisms could also explain the

461 small bioaccumulation of Gd-contrast agents observed in *Corbicula fluminea* after *in situ*
462 exposure. The D<sub>REE</sub> calculated for the dissolved Gd fraction (Figure 4B) show a strong negative
463 Gd anomaly at the WWTP Downstream site (D<sub>REE</sub>=720), matching the results obtained for the
464 BCFs, and support the idea that medical-origin Gd<sub>anth</sub>, mainly present in the dissolved fraction, is
465 less bioavailable than natural Gd. The patterns obtained for particulate D<sub>REE</sub> (Figure 4C) show a
466 positive anomaly in Gd at the WWTP Downstream site indicating preferential assimilation of this
467 element in the particulate fraction. This anomaly is not visible in the particulate fraction of water
468 from the Jalle River and the individuals at the Thil site do not show a positive anomaly in Gd for
469 particulate D<sub>REE</sub>.

470 **5. Summary and Perspectives**

471 This study has provided information about the bioavailability of natural REEs in *Corbicula
472 fluminea* thanks to the determination of natural BCFs but also of the D<sub>REE</sub> specific to the dissolved
473 and particulate fractions. The orders of bioavailability in *Corbicula fluminea* have been
474 determined with, for the dissolved fraction: MREEs > LREEs > HREEs and for the particulate
475 fraction: MREEs > LREEs = HREEs. Moreover, this study highlights the importance of the
476 particulate fraction in the bioavailability of natural REEs in benthic bivalves such as *Corbicula
477 fluminea*, particularly with respect to HREEs. It would therefore be interesting in future studies,
478 to determine the associated entry pathways and whether there is fractioning of these natural REEs
479 between the organs in order to have an overview of the distribution and management of REEs by
480 organisms.

481 This study has also brought to light anomalies in Gd in the water of an urban river, both for the
482 dissolved and total fractions. This positive anomaly in Gd was observed downstream of the
483 WWTP effluents and the source of this anthropogenic Gd has been attributed to its use as a
484 contrast agent for MRI. Despite the bioavailability of Gd<sub>anth</sub> being lower than that of Gd<sub>nat</sub> it was
485 also observed in the soft tissue of caged *Corbicula fluminea* downstream of the WWTP effluent.
486 The present work providing first profiles of REEs in the soft tissue of *Corbicula fluminea*, as part
487 of biomonitoring for medical-origin Gd contaminations. *Corbicula fluminea* thus appears to be an
appropriate model species for *in situ* monitoring of REE contaminations such as medical-origin Gd. The method used in this work would thus appear to be operational and it would be appropriate to check whether *Corbicula fluminea* could be used in the context of other anthropogenic REE contaminations (e.g. Ce, La). The Gd anomalies observed in caged organisms on the Jalle River highlight the overall nature of contamination by Gd<sub>anth</sub>, including in small, urban rivers. Indeed, today, a very large number of hydrosystems throughout the world are concerned by anomalies in anthropogenic REEs and particularly medical-origin Gd. Moreover, current public health policies are encouraging a constant increase in the number of MRI scanners: for example, in France, they increased by a mean of 10% per year between 2003 and 2017 (Lerat-Hardy et al., 2019). In this context, the quantities of medical Gd in aquatic systems are going to increase in future years, leading to risks in ecosystems subject to urban pressure. Given that Gd<sub>anth</sub> is bioavailable for bivalves and particularly those living in the water column (Akagi and Edanami, 2017), it is possible that Gd<sub>anth</sub> will enter the human trophic chain *via* cultivated species from shellfish farms, thus presenting potential health risks and significant economic problems. It would thus appear to be necessary to consider the establishment of environmental standards for this type of contamination over the next few years.

## 6. Acknowledgments

This work has benefited from the support by the Water Regional Agency (Agence de l'Eau Adour-Garonne) and "Agence Française pour la Biodiversité" with the National Project REGARD: "Comprehensive and integrated program against micropollutants (city of Bordeaux)".
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800

## Figure, table and supplementary data captions

801

Fig. 1. Location of sampling sites (black circles) in the Jalle River watershed (green outline). The colored background correspond to distinct pedologies (orange – podzols; blue – calcareous soils).

802

803

Characterized WWTP effluent (black arrow) and uncharacterized WWTP effluent (empty triangle).

804

805

Fig. 2. EUS-normalized concentration patterns at each sampling time and each sampling site for dissolved (A), total (B) and particulate phases (C). EUS-normalized patterns of discharge-weighted REE concentrations for each phases (D).

806

807

808

Fig. 3. EUS-normalized concentration patterns for soft bodies of *Corbicula fluminea* (mean; n=5) at Thil and WWTP Downstream stations (A). Mean REE patterns of WWTP Downstream organisms normalized by Thil organisms (B).

809

810
Fig. 4. (A) Bioconcentration factors of natural REEs (grey curves) and overall REEs (black curves). (B) Natural dissolved D<sub>REE</sub> (grey curves) and overall dissolved D<sub>REE</sub> (black curves). (C) Natural particulate D<sub>REE</sub> (grey curves) and overall particulate D<sub>REE</sub> (black curves).

Table 1. Quality control using the certified reference material SLRS-6 (n=72; mean ± SD;
Yeghicheyan et al., 2019)

Table 2. REE concentrations (ng.L⁻¹) and water discharges (Q; m³.s⁻¹) of the sampling sites.
Estimated natural (Gd<sub>nat</sub>) and anthropogenic (Gd<sub>anth</sub>) concentrations of Gd (ng.L⁻¹) obtained by
modeling. REE concentrations of the three sampling times and the three sampling phases
(dissolved, total, particulate). Discharge-weighted concentrations (values) for each sites and
phases. REE concentrations of the WWTP effluents for the dissolved phase (n=5; mean ± SD).
REE concentrations (ng.gDW⁻¹) and Condition Index (CI; %) for the soft bodies of *Corbicula
fluminea* transplanted in the Jalle River (n=5; mean ± SE).

Sm(1) = samarium concentrations (values) are obtained with polynomial regression models for
Jalle River waters and WWTP effluents.

Supplementary data. Recovery efficiency (% ± RSD) for REEs concentrations of certified
reference material SLRS-6 (n=72). Detection limit for REEs analyzed in inorganic and biological
samples (n=27; mean). Histograms of certified and measured concentrations for the certified
reference material SLRS-6 (n=72; mean ± SD).
<figure><img src="image_1.png" /></figure>

Jalle River Watershed

THIL

△

WWTP
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>
<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>
<table><thead><tr><th>SLRS-6<br>(ng.L<sup>-1</sup>)</th><th>Certified<br>values</th><th>Measured<br>values</th></tr></thead><tbody><tr><td><strong>La</strong></td><td>248 ± 12.1</td><td>235 ± 19.0</td></tr><tr><td><strong>Ce</strong></td><td>292 ± 15.1</td><td>281 ± 22.5</td></tr><tr><td><strong>Pr</strong></td><td>59.1 ± 1.9</td><td>58.6 ± 4.96</td></tr><tr><td><strong>Nd</strong></td><td>227 ± 9.4</td><td>221 ± 12.7</td></tr><tr><td><strong>Sm</strong></td><td>39.5 ± 1.7</td><td>38.4 ± 2.31</td></tr><tr><td><strong>Eu</strong></td><td>7.26 ± 0.35</td><td>6.23 ± 0.71</td></tr><tr><td><strong>Gd</strong></td><td>31.6 ± 2.5</td><td>28.1 ± 1.72</td></tr><tr><td><strong>Tb</strong></td><td>4.07 ± 0.27</td><td>3.46 ± 0.25</td></tr><tr><td><strong>Dy</strong></td><td>21.9 ± 1.1</td><td>19.5 ± 1.39</td></tr><tr><td><strong>Ho</strong></td><td>4.3 ± 0.3</td><td>3.93 ± 0.39</td></tr><tr><td><strong>Er</strong></td><td>12.4 ± 0.7</td><td>11.0 ± 0.76</td></tr><tr><td><strong>Tm</strong></td><td>1.79 ± 0.18</td><td>1.56 ± 0.17</td></tr><tr><td><strong>Yb</strong></td><td>11.2 ± 0.7</td><td>10.2 ± 1.04</td></tr><tr><td><strong>Lu</strong></td><td>1.91 ± 0.23</td><td>1.59 ± 0.28</td></tr></tbody></table>
<table><thead><tr><th>Jalle River</th><th>Date</th><th>Q</th><th>La</th><th>Ce</th><th>Pr</th><th>Nd</th><th>Sm<sup>(1)</sup></th><th>Eu</th><th>Gd</th><th>Tb</th><th>Dy</th><th>Ho</th><th>Er</th><th>Tm</th><th>Yb</th><th>Lu</th><th>Gd<sub>nat</sub></th><th>Gd<sub>anth</sub></th></tr></thead><tbody><tr><td rowspan="10">Dissolved</td><td rowspan="4">THIL</td><td>March</td><td>6.46</td><td>219.2</td><td>386.4</td><td>65.1</td><td>245.6</td><td>46.3</td><td>11.9</td><td>46.0</td><td>6.6</td><td>42.9</td><td>10.0</td><td>32.0</td><td>4.9</td><td>33.7</td><td>5.8</td><td>40.5</td><td>5.5</td></tr><tr><td>April</td><td>1.54</td><td>126.5</td><td>196.3</td><td>35.8</td><td>134.9</td><td>26.4</td><td>6.4</td><td>28.1</td><td>3.9</td><td>26.0</td><td>6.1</td><td>19.8</td><td>3.1</td><td>21.6</td><td>3.9</td><td>26.1</td><td>2.0</td></tr><tr><td>June</td><td>0.71</td><td>104.6</td><td>197.8</td><td>29.6</td><td>116.6</td><td>23.8</td><td>5.5</td><td>26.7</td><td>3.5</td><td>22.3</td><td>4.9</td><td>15.9</td><td>2.7</td><td>19.2</td><td>3.2</td><td>22.1</td><td>4.6</td></tr><tr><td>Weighted</td><td>-</td><td><strong>127.6</strong></td><td><strong>217.1</strong></td><td><strong>36.4</strong></td><td><strong>139.3</strong></td><td><strong>27.5</strong></td><td><strong>6.6</strong></td><td><strong>29.5</strong></td><td><strong>4.0</strong></td><td><strong>26.3</strong></td><td><strong>6.0</strong></td><td><strong>19.6</strong></td><td><strong>3.1</strong></td><td><strong>21.9</strong></td><td><strong>3.8</strong></td><td><strong>26.0</strong></td><td><strong>3.4</strong></td></tr><tr><td rowspan="4">WWTP Downstream</td><td>March</td><td>5.78</td><td>238.4</td><td>395.8</td><td>70.1</td><td>264.3</td><td>52.2</td><td>13.1</td><td>49.1</td><td>7.0</td><td>46.3</td><td>10.6</td><td>33.7</td><td>5.5</td><td>38.4</td><td>6.1</td><td>44.2</td><td>4.9</td></tr><tr><td>April</td><td>1.41</td><td>78.6</td><td>116.3</td><td>23.8</td><td>89.5</td><td>17.3</td><td>4.2</td><td>104.8</td><td>2.8</td><td>19.4</td><td>4.6</td><td>15.2</td><td>2.5</td><td>17.2</td><td>3.6</td><td>18.2</td><td>86.6</td></tr><tr><td>June</td><td>0.66</td><td>66.1</td><td>119.0</td><td>18.5</td><td>84.6</td><td>16.4</td><td>3.4</td><td>27.4</td><td>2.3</td><td>16.9</td><td>3.8</td><td>12.5</td><td>2.1</td><td>16.8</td><td>2.8</td><td>14.6</td><td>12.7</td></tr><tr><td>Weighted</td><td>-</td><td><strong>90.5</strong></td><td><strong>147.0</strong></td><td><strong>26.6</strong></td><td><strong>106.1</strong></td><td><strong>20.6</strong></td><td><strong>4.8</strong></td><td><strong>67.9</strong></td><td><strong>3.0</strong></td><td><strong>21.2</strong></td><td><strong>4.9</strong></td><td><strong>16.1</strong></td><td><strong>2.7</strong></td><td><strong>19.3</strong></td><td><strong>3.5</strong></td><td><strong>19.6</strong></td><td><strong>48.4</strong></td></tr><tr><td rowspan="10">Total</td><td rowspan="4">THIL</td><td>March</td><td>6.46</td><td>666.1</td><td>1453.5</td><td>187.6</td><td>727.2</td><td>136.3</td><td>32.1</td><td>130.2</td><td>18.0</td><td>111.8</td><td>22.7</td><td>69.0</td><td>9.8</td><td>64.8</td><td>9.9</td><td>120.6</td><td>9.7</td></tr><tr><td>April</td><td>1.54</td><td>411.6</td><td>860.6</td><td>112.3</td><td>445.7</td><td>87.3</td><td>20.1</td><td>81.0</td><td>11.2</td><td>69.2</td><td>14.1</td><td>45.2</td><td>6.5</td><td>49.8</td><td>7.3</td><td>78.2</td><td>2.8</td></tr><tr><td>June</td><td>0.71</td><td>283.1</td><td>599.8</td><td>77.0</td><td>294.9</td><td>56.4</td><td>12.2</td><td>58.0</td><td>7.7</td><td>45.7</td><td>9.3</td><td>30.3</td><td>4.0</td><td>30.8</td><td>4.9</td><td>50.0</td><td>8.0</td></tr><tr><td>Weighted</td><td>-</td><td><strong>387.2</strong></td><td><strong>819.1</strong></td><td><strong>106.2</strong></td><td><strong>415.2</strong></td><td><strong>80.2</strong></td><td><strong>18.2</strong></td><td><strong>77.1</strong></td><td><strong>10.5</strong></td><td><strong>64.3</strong></td><td><strong>13.1</strong></td><td><strong>41.8</strong></td><td><strong>5.9</strong></td><td><strong>43.8</strong></td><td><strong>6.6</strong></td><td><strong>71.4</strong></td><td><strong>5.6</strong></td></tr><tr><td rowspan="4">WWTP Downstream</td><td>March</td><td>5.78</td><td>470.4</td><td>977.4</td><td>134.4</td><td>532.2</td><td>96.8</td><td>24.5</td><td>92.3</td><td>13.2</td><td>83.2</td><td>16.9</td><td>53.8</td><td>7.5</td><td>55.7</td><td>7.4</td><td>86.5</td><td>5.9</td></tr><tr><td>April</td><td>1.41</td><td>251.6</td><td>513.6</td><td>72.6</td><td>287.9</td><td>54.8</td><td>13.2</td><td>132.5</td><td>7.3</td><td>47.8</td><td>10.0</td><td>31.4</td><td>4.9</td><td>35.2</td><td>5.7</td><td>45.7</td><td>86.9</td></tr><tr><td>June</td><td>0.66</td><td>187.6</td><td>362.3</td><td>50.1</td><td>195.7</td><td>37.3</td><td>9.2</td><td>46.1</td><td>5.1</td><td>33.2</td><td>7.2</td><td>21.3</td><td>3.5</td><td>23.1</td><td>3.9</td><td>29.8</td><td>16.3</td></tr><tr><td>Weighted</td><td>-</td><td><strong>249.2</strong></td><td><strong>502.2</strong></td><td><strong>70.1</strong></td><td><strong>276.9</strong></td><td><strong>52.2</strong></td><td><strong>12.8</strong></td><td><strong>93.7</strong></td><td><strong>7.1</strong></td><td><strong>45.7</strong></td><td><strong>9.6</strong></td><td><strong>29.7</strong></td><td><strong>4.6</strong></td><td><strong>32.6</strong></td><td><strong>5.1</strong></td><td><strong>43.7</strong></td><td><strong>50.0</strong></td></tr><tr><td rowspan="10">Particulate</td><td rowspan="4">THIL</td><td>March</td><td>6.46</td><td>446.9</td><td>1067.1</td><td>122.5</td><td>481.6</td><td>89.9</td><td>20.2</td><td>84.3</td><td>11.5</td><td>68.9</td><td>12.7</td><td>37.0</td><td>4.9</td><td>31.1</td><td>4.1</td><td>80.1</td><td>4.2</td></tr><tr><td>April</td><td>1.54</td><td>285.2</td><td>664.3</td><td>76.4</td><td>310.8</td><td>60.9</td><td>13.8</td><td>52.9</td><td>7.3</td><td>43.2</td><td>8.0</td><td>25.4</td><td>3.5</td><td>28.2</td><td>3.5</td><td>52.1</td><td>0.8</td></tr><tr><td>June</td><td>0.71</td><td>178.5</td><td>402.0</td><td>47.5</td><td>178.3</td><td>32.6</td><td>6.8</td><td>31.3</td><td>4.2</td><td>23.4</td><td>4.3</td><td>14.4</td><td>1.3</td><td>11.6</td><td>1.7</td><td>27.9</td><td>3.4</td></tr><tr><td>Weighted</td><td>-</td><td><strong>259.6</strong></td><td><strong>602.1</strong></td><td><strong>69.7</strong></td><td><strong>275.9</strong></td><td><strong>52.7</strong></td><td><strong>11.6</strong></td><td><strong>47.6</strong></td><td><strong>6.5</strong></td><td><strong>38.0</strong></td><td><strong>7.0</strong></td><td><strong>22.2</strong></td><td><strong>2.7</strong></td><td><strong>21.9</strong></td><td><strong>2.8</strong></td><td><strong>45.4</strong></td><td><strong>2.2</strong></td></tr><tr><td rowspan="4">WWTP Downstream</td><td>March</td><td>5.78</td><td>232.0</td><td>581.5</td><td>64.4</td><td>267.9</td><td>44.6</td><td>11.4</td><td>43.3</td><td>6.1</td><td>36.9</td><td>6.3</td><td>20.2</td><td>2.0</td><td>17.2</td><td>1.3</td><td>42.3</td><td>1.0</td></tr><tr><td>April</td><td>1.41</td><td>173.0</td><td>397.3</td><td>48.8</td><td>198.4</td><td>37.5</td><td>9.0</td><td>27.7</td><td>4.5</td><td>28.4</td><td>5.4</td><td>16.2</td><td>2.4</td><td>18.1</td><td>2.1</td><td>27.4</td><td>0.3</td></tr><tr><td>June</td><td>0.66</td><td>121.5</td><td>243.3</td><td>31.6</td><td>111.2</td><td>20.9</td><td>5.9</td><td>18.7</td><td>2.9</td><td>16.3</td><td>3.4</td><td>8.8</td><td>1.4</td><td>6.3</td><td>1.1</td><td>15.2</td><td>3.5</td></tr><tr><td>Weighted</td><td>-</td><td><strong>158.7</strong></td><td><strong>355.2</strong></td><td><strong>43.5</strong></td><td><strong>170.9</strong></td><td><strong>31.6</strong></td><td><strong>8.0</strong></td><td><strong>25.8</strong></td><td><strong>4.0</strong></td><td><strong>24.5</strong></td><td><strong>4.7</strong></td><td><strong>13.7</strong></td><td><strong>2.0</strong></td><td><strong>13.3</strong></td><td><strong>1.6</strong></td><td><strong>24.1</strong></td><td><strong>1.7</strong></td></tr><tr><td rowspan="2">WWTP effluent</td><td></td><td></td><td>7.5±</td><td>16.0±</td><td>1.9±</td><td>9.5±</td><td>8.1±</td><td></td><td>326±</td><td>0.4±</td><td>3.2±</td><td>0.9±</td><td>4.1±</td><td>0.7±</td><td>6.9±</td><td>1.2±</td><td>2.0±</td><td>324±</td></tr><tr><td></td><td></td><td>2.4</td><td>5.1</td><td>0.9</td><td>4.4</td><td>1.6</td><td></td><td>125</td><td>0.3</td><td>2.3</td><td>0.7</td><td>3.3</td><td>0.5</td><td>5.3</td><td>1.0</td><td>1.3</td><td>126</td></tr><tr><td colspan="2"></td><td>CI (%)</td><td>La</td><td>Ce</td><td>Pr</td><td>Nd</td><td>Sm</td><td>Eu</td><td>Gd</td><td>Tb</td><td>Dy</td><td>Ho</td><td>Er</td><td>Tm</td><td>Yb</td><td>Lu</td><td>Gd<sub>nat</sub></td><td>Gd<sub>anth</sub></td></tr><tr><td rowspan="2">Corbiculara fluminea</td><td rowspan="2">THIL</td><td></td><td>6.3±</td><td>410±</td><td>760±</td><td>109±</td><td>493±</td><td>113±</td><td>29±5</td><td>110±</td><td>13±3</td><td>79±15</td><td>16±3</td><td>41±8</td><td>5.0±1</td><td>28±6</td><td>4.2±</td><td>109±</td><td>1.5±1</td></tr><tr><td></td><td>0.4</td><td>87</td><td>175</td><td>24</td><td>96</td><td>21</td><td></td><td>19</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.9</td><td>19</td><td></td></tr><tr><td rowspan="2">WWTP Downstream</td><td></td><td>7.0±</td><td>172±</td><td>320±</td><td>46±4</td><td>209±</td><td>47±4</td><td>11±1</td><td>49±4</td><td>5.5±</td><td>32±3</td><td>6.5±</td><td>17±1</td><td>2.1±</td><td>11±</td><td>1.8±</td><td>45±4</td><td>4.1±</td></tr><tr><td></td><td>0.4</td><td>15</td><td>28</td><td></td><td>18</td><td></td><td></td><td></td><td></td><td>0.5</td><td></td><td>0.6</td><td></td><td>0.2</td><td>0.8</td><td>0.1</td><td>0.7</td></tr></tbody></table>
<figure><img src="image_11.png" /></figure>

WWTP Effluent

Thil site

Gd<sub>anth</sub>

Corbicula fluminea