Dissolved metal adsorption capacities and fractionation in filter materials for use in stormwater bioretention facilities

Probably not a substantial claim: may not pass S3 (load-bearing).

Previous studies have found that percentages of most metals in exchangeable fractions of stormwater sediments (pond sediments, gully pot sediments, road dust etc.) are low or non-detectable.

“Previous studies have found that percentages of most metals in exchangeable fractions of stormwater sediments (pond sediments, gully pot sediments, road dust etc.) are low or non-detectable (Marsalek and Marsalek, 1997; Karlsson et al., 2016; Jayarathne et al., 2017).”

• cites Marsalek and Marsalek, 1997 sourceNot checked — no full text of the source
• cites Karlsson et al., 2016 sourceNot checked — no full text of the source
• cites Jayarathne et al., 2017 sourceDisputed

  Section 3.3.1 reports high exchangeable fractions for Cd (~53%) and Zn (~56%), and describes Pb’s ~14% exchangeable fraction as significant; it also reports Cu at ~19% and Mn at ~14%. Although Cr and Ni are concentrated in the residual fraction, the paper does not characterize the exchangeable percentages of most metals in road dust as low or non-detectable. The cited paper studies road dust, not pond or gully pot sediments. (LLM, conf=0.87)

  Checked by a reasoning model — may be wrong.

  Experimental — accuracy not yet measured

May combine two claims.

Conflicting results have been observed in previous studies regarding removal of dissolved metals in stormwater bioretention systems: some found efficient retention, while others found substantial leaching.

“Conflicting results have been observed in previous studies regarding removal of dissolved metals in stormwater bioretention systems. Some have found that dissolved metals are efficiently retained (e.g. Blecken et al., 2011; Wang et al., 2017), while others have found substantial leaching (e.g. Muthanna et al., 2007; Hatt et al., 2008; Søberg et al., 2017).”

• cites Blecken et al., 2011 sourceNot checked — no full text of the source
• cites Wang et al., 2017 sourceSupported
• cites Muthanna et al., 2007 sourceNot checked — no full text of the source

May combine two claims.

In an evaluation of two full-scale bioretention cells at North Carolina State University, Luell (2011) observed relatively low removal of total Cu (23-43%), dissolved Cu (17-49%), and total Zn (79%).

“In an evaluation of two full-scale bioretention cells at North Carolina State University, Luell (2011) observed relatively low removal of total Cu (23–43%), dissolved Cu (17–49%), and total Zn (79%).”

• cites Luell (2011)Supported

May combine two claims.

The comparison between the present lab-scale study and previous field-scale studies is limited because field-scale systems are exposed to numerous uncontrolled factors and account for particulate-bound metals, unlike the current study.

“However, it should be noted that Winston et al. (2015) and Luell (2011) focused on full-scale systems exposed to numerous, uncontrolled factors in contrast to the lab-scale systems maintained under controlled conditions in the present study. Additionally, field-scale tests also account for particulate bond metals, unlike the current study.”

• cites Winston et al. (2015)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Luell (2011)Partly supported

  Section 3.2 (page unavailable) identifies this as a field-scale study, and the sampling protocol records both total and dissolved metals, so its measurements include particulate-bound metals. The claim about numerous uncontrolled factors is less well supported: Section 3.2 says the cells shared a drainage source specifically to eliminate factors such as climate and surrounding land use from the comparison. The source does not assess the citing paper’s lab-scale study. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Probably not a substantial claim: may not pass S3 (load-bearing).

Jayarathne et al. (2017) found approximately 50% of adsorbed Zn and Cd in the exchangeable fraction.

“However, Jayarathne et al. (2017) found approximately 50% of adsorbed Zn and Cd in the exchangeable fraction.”

• cites Jayarathne et al. (2017) sourceSupported

Probably not a substantial claim: may not pass S3 (load-bearing).

In a laboratory-scale study of Cd removal by four bioretention filter materials (fine sand, zeolite, sand and quartz sand), accumulated Cd was detected mainly in the residual form.

“In contrast, in a laboratory-scale study of Cd removal by four bioretention filter materials (fine sand, zeolite, sand and quartz sand) accumulated Cd was detected mainly in the residual form (Wang et al., 2017).”

• cites Wang et al., 2017 sourcePartly supported

  Section 3.5.3 reports that the majority of Cd in the four media was in the residual fraction. However, the study identifies the media as sand, zeolite, sandy loam, and quartz sand, each mixed with lignin—not fine sand, zeolite, sand, and quartz sand as claimed (Sections 2.2 and 3.5.3). (LLM, conf=0.90)

  Experimental — accuracy not yet measured

May combine two claims.

All materials adsorbed essentially all available metals at the two lowest initial concentrations, whereas differences in adsorption capacity between materials appeared at the higher initial concentrations.

“Thus, all materials adsorbed essentially all available metals at the two lowest initial concentrations, whereas differences in adsorption capacity between materials appeared at the higher initial concentrations.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The pH of LTU-Top and NC-USA were 6.1 and 6.3, respectively.

“As shown in Table 2, the pH of LTU-Top and NC-USA were 6.1 and 6.3, respectively, the pH of DWA-chalk was 9.2, and the pH of all the other materials ranged from 7.7 to 8.8.”

May combine two claims.

Hasselfors had by far the largest D50 and second lowest Cu, so it is much coarser (mainly gravel) and more heterogeneous material than the others.

“Hasselfors had by far the largest D50 and second lowest Cu (Table 2), so it is much coarser (mainly gravel) and more heterogeneous material than the others (Fig. 1).”

Probably not a substantial claim: may not pass S3 (load-bearing).

The pH of all other materials (besides LTU-Top, NC-USA, DWA-chalk) ranged from 7.7 to 8.8.

“As shown in Table 2, the pH of LTU-Top and NC-USA were 6.1 and 6.3, respectively, the pH of DWA-chalk was 9.2, and the pH of all the other materials ranged from 7.7 to 8.8.”

May combine two claims.

Sand-based materials LTU-TOP, DWA and DWA-chalk without biochar additives have low OM contents and small SSA.

“In contrast, the sand-based materials LTU-TOP, DWA and DWA-chalk without biochar additives have low OM contents and small SSA.”

May combine two claims.

Despite differences between materials, the adsorption process was relatively fast; within an hour, most materials had adsorbed >90% of the metals, and half-life times of less than a minute were observed.

“Despite differences between materials, the adsorption process was relatively fast. Within an hour, most of the materials had adsorbed >90% of the metals (Fig. 3) and half-life times of less than a minute were observed (Table S2).”

May combine two claims.

In the present study, KB-OHIO showed excellent adsorption of all tested metals and was consistently amongst the top three materials.

“In the present study, KB-OHIO showed excellent adsorption of all tested metals and was consistently amongst the top three materials (Fig. 2).”

May combine two claims.

DWA-chalk had a lower initial adsorption rate and longer half-life time than the remaining six materials, but equally high equilibrium adsorbate concentrations.

“DWA-chalk had a lower initial adsorption rate and longer half-life time than the remaining six materials (Table S2), but equally high equilibrium adsorbate concentrations (Fig. 3; Table S2).”

May combine two claims.

Hekla and Hekla-B had slower and lower adsorption of Cr from multi-metal solutions, and thus the longest half-life times and lowest equilibrium adsorbate concentrations for Cr.

“Hekla and Hekla-B had slower and lower adsorption of Cr from multi-metal solutions (Fig. 3), and thus the longest half-life times and lowest equilibrium adsorbate concentrations for Cr (Table S2).”

May combine two claims.

The trends were less clear for adsorption of Zn, Ni and Cd from multi-metal solutions and were only supported by the Dubinin-Radushkevich model constants, despite the Langmuir isotherm providing a better fit for Ni and relatively high R2 values for Zn and Cd.

“However, the trends were less clear for adsorption of Zn, Ni and Cd from multi-metal solutions, and were only supported by the Dubinin-Radushkevich model constants, despite the Langmuir isotherm providing a better fit for adsorption of Ni, and relatively high R2 values for adsorption of Zn and Cd from the multi-metal solutions.”

May combine two claims.

For KB-OHIO and BN-OHIO, the Langmuir maximum adsorption capacity constant, Dubinin-Radushkevich adsorption capacity constant and Temkin heat of adsorption constant were highest, while the Temkin model constant and Dubinin-Radushkevich mean sorption energy were lowest.

“For example, the Langmuir maximum adsorption capacity constant, Dubinin-Radushkevich adsorption capacity constant and Temkin heat of adsorption constant were highest for these materials, while the Temkin model constant and Dubinin-Radushkevich mean sorption energy were lowest (Table S1).”

May combine two claims.

Substantial percentages of Cr (but no other metals) adsorbed by several materials were detected in fractions IV and V; for example, 18% of Cr adsorbed to fraction V in Hasselfors and 15% to fraction IV in LTU-TOP.

“Moreover, substantial percentages of Cr (but no other metals) adsorbed by several materials were detected in fractions IV and V. For example, 18% of Cr adsorbed to fraction V (stable organic forms and sulfides) in Hasselfors and 15% adsorbed to fraction IV (more crystalline Fe-oxides) in LTU-TOP (Fig. 4).”

Probably not a substantial claim: may not pass S3 (load-bearing).

The duplicates did not deviate considerably from each other.

“This is further supported by the fact that the duplicates did not deviate considerably from each other.”

May combine two claims. The quote only partly states this claim.

For adsorption of Cu from single and multi-metal solutions, Zn from single-metal solutions and Pb from multi-metal solutions, the Langmuir maximum adsorption capacity constant, Dubinin-Radushkevich adsorption capacity constant and Temkin heat of adsorption constant were consistently lowest for LTU-TOP, DWA and NC-USA, while the Temkin model constant and Dubinin-Radushkevich mean sorption energy, 0

“For example, the Langmuir maximum adsorption capacity constant, the Dubinin-Radushkevich adsorption capacity constant and the Temkin heat of adsorption constant for adsorption of Cu from single and multi-metal solutions, Zn from single-metal solutions and Pb from multi-metal solutions were consistently lowest for these three filter materials. Accordingly, the Temkin model constant and Dubinin-Rad”

May combine two claims.

For multi-metal solutions, the Langmuir isotherm provided the best fit for Cu, Ni and Pb adsorption; the Dubinin-Radushkevich isotherm for Zn and Cd; and the Temkin isotherm for Cr.

“In these cases: the Langmuir isotherm provided the best fit for Cu, Ni and Pb adsorption; the Dubinin-Radushkevich isotherm the best fit for Zn and Cd adsorption; and the Temkin isotherm the best fit for Cr adsorption (Table S1).”

May combine two claims.

For the two single-metal solutions, the Langmuir isotherms generally provided the best fit, and all isotherms had high (>0.8) R2 values.

“For the two single-metal solutions, the Langmuir isotherms generally provided the best fit. However, for the single-metal solutions, all isotherms had high (>0.8) R2 values (Table S1).”

May combine two claims.

Adsorption was generally fast and within an hour more than 90% of most metals was adsorbed.

“Furthermore, adsorption was generally fast and within an hour more than 90% of most metals was adsorbed.”

May combine two claims.

The materials with the highest metal adsorption (KB-OHIO, BN-OHIO and Orbicon) all have relatively high pH and SSA, low to medium OM contents, and are classified as sand with relatively uniform grainsize.

“The materials with the highest metal adsorption (KB–OHIO, BN-OHIO and Orbicon) all have relatively high pH and SSA, low to medium OM contents, and are classified as sand with relatively uniform grainsize (Table 2).”

May combine two claims.

The Temkin isotherm heat of adsorption constants and Dubinin-Radushkevich mean sorption energies obtained in this study were <1.2 and <5.1 KJ/mol, respectively, indicative of physical sorption processes.

“The Temkin isotherm heat of adsorption constants and Dubinin-Radushkevich mean sorption energies obtained in this study were <1.2 and < 5.1 KJ/mol, respectively (Table S1), indicative of physical sorption processes.”

May combine two claims.

Adsorption parameters of both Hasselfors and Hekla-B (the materials containing biochar) were moderate and did not substantially differ from those of the other materials.

“Further, adsorption parameters of both Hasselfors and Hekla-B (the materials containing biochar) were moderate and did not substantially differ from those of the other materials (Fig. 2, Fig. 3).”

May combine two claims.

High percentages of the adsorbed metals were found in the potentially leachable fractions, with obvious implications for long-term performance of the materials, their functionality under varying conditions and the maintenance of bioretention facilities.

“High percentages of the adsorbed metals were found in the potentially leachable fractions, with obvious implications for long-term performance of the materials, their functionality under varying conditions and the maintenance of bioretention facilities.”

May combine two claims.

Conversely, DWA, LTU-TOP and NC-USA, the materials with the lowest metal adsorption, have markedly lower pH than the other materials, small SSA and low OM contents.

“Conversely, DWA, LTU-TOP and NC-USA, the materials with the lowest metal adsorption, have markedly lower pH than the other materials, small SSA and low OM contents (Table 2).”

May combine two claims.

The Langmuir separation factors indicate that the adsorption processes were favorable, but not irreversible (0<RL < 1), and thus largely physical.

“The Langmuir separation factors (Table S1) also indicate that the adsorption processes were favorable, but not irreversible (0<RL < 1), and thus largely physical.”

May combine two claims.

All the tested materials adsorbed metals, although as metal concentrations increased and metal solutions became more complex the adsorption of some metals decreased.

“All the tested materials adsorbed metals, although as metal concentrations increased and metal solutions became more complex the adsorption of some metals decreased.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

All experiments (except sequential leaching) were run in duplicate, with an extra replicate run if results differed markedly.

“All experiments (except the sequential leaching) were run in duplicate, however, if results differed markedly, an extra replicate was run (which was only the case in a very few instances).”

Probably not a substantial claim: may not pass S3 (load-bearing).

Metals can negatively affect the ecological status of surface waters depending on their prevalence, toxicity and resistance to degradation and/or chemical transformation.

“Depending on their prevalence, toxicity and resistance to degradation and/or chemical transformation metals might negatively affect the ecological status of surface waters (Søberg et al., 2017).”

• cites Søberg et al., 2017 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The addition of chalk is recommended to enhance metal adsorption and compensate for low OM content.

“The addition of chalk is recommended to enhance metal adsorption and compensate for low OM content (Grotehusmann et al., 2016; DWA, 2005).”

• cites Grotehusmann et al., 2016Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites DWA, 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Reported removals of dissolved metals are fewer and contradictory, including both efficient removal and significant leaching.

“However, reported removals of dissolved metals are fewer and contradictory including both efficient removal and significant leaching (e.g. Muthanna et al., 2007; Søberg et al., 2017).”

• cites Muthanna et al., 2007 sourceNot checked — no full text of the source
• cites Søberg et al., 2017 sourceNot checked — no full text of the source

May combine two claims.

Leaching from the materials did not substantially influence the results because concentrations detected in initial leaching tests are much lower than concentrations used in batch adsorption, batch kinetic and sequential extraction experiments.

“Unfortunately it was not possible to clarify the reason(s) for the leaching of Cu and Zn in the controls, but the concentrations detected in the initial leaching tests (Table 3) are much lower than concentrations used in the batch adsorption, batch kinetic and sequential extraction experiments, so leaching from the materials did not substantially influence the results.”

May combine two claims.

Dissolved metals are more difficult to remove and usually more bioavailable compared to particulate metals, thereby posing a greater risk.

“Although dissolved metals are more difficult to remove and usually more bioavailable compared to particulate metals, thereby posing a greater risk (Fassman et al., 2013; Flanagan et al., 2019), bioretention studies have generally focused on total metal removal (Hunt et al., 2012).”

• cites Fassman et al., 2013Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Flanagan et al., 2019 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S2 (checkable).

The filter material should have a hydraulic conductivity ensuring both adequate retention for adsorption to occur and adequate infiltration capacity to avoid overflow.

“The material should have a hydraulic conductivity ensuring both adequate retention for adsorption to occur and adequate infiltration capacity to avoid overflow (Fassman et al., 2013).”

• cites Fassman et al., 2013Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Probably not a substantial claim: may not pass S3 (load-bearing).

Urban stormwater runoff is a major source of metal contamination in receiving water bodies.

“urban stormwater runoff is considered a major source of metal contamination in receiving water bodies (e.g. Becouze-Lareure et al., 2019).”

• cites Becouze-Lareure et al., 2019 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

A large number of field and laboratory studies have shown efficient total metal removal for bioretention systems, often exceeding 80-90%.

“A large number of field and laboratory studies have shown efficient total metal removal for bioretention systems, often exceeding 80–90% (e.g. Hatt et al., 2008; Søberg et al., 2017).”

• cites Hatt et al., 2008 sourceNot checked — no full text of the source
• cites Søberg et al., 2017 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

Vegetation contributes to total metal removal in stormwater bioretention systems.

“The vegetation has been shown to contribute to the total metal removal in stormwater bioretention systems (Muthanna et al., 2007; Sun and Davis, 2007; Read et al., 2008).”

• cites Muthanna et al., 2007 sourceNot checked — no full text of the source
• cites Sun and Davis, 2007 sourceNot checked — no full text of the source
• cites Read et al., 2008 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

The filter material should have physical and chemical properties to support plant life, enhance treatment and avoid clogging.

“It should have physical and chemical properties to support plant life, enhance treatment and avoid clogging (Fassman et al., 2013).”

• cites Fassman et al., 2013Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Classified as probably not a substantial claim.

Controls (solution without filter material) were included in all runs.

“Controls (solution without filter material) were included in all runs.”

May combine two claims.

The bioretention systems examined in the cited studies were relatively young (<2 years) and found metals to be adsorbed in the top 5 cm of the filter material, so these systems were far from saturated with metals.

“Moreover, the bioretention systems examined in the cited studies (Muthanna et al., 2007; Hatt et al., 2008; Blecken et al., 2011; Wang et al., 2017; Søberg et al., 2017) were relatively young (<2 years) and found metals to be adsorbed in the top 5 cm of the filter material. Hence, these systems were far from saturated with metals.”

• cites Muthanna et al., 2007 sourceNot checked — no full text of the source
• cites Hatt et al., 2008 sourceNot checked — no full text of the source
• cites Blecken et al., 2011 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing).

Metals primarily accumulate in the top 5 cm of bioretention filter materials.

“The latter becomes evident considering that metals primarily accumulate in the top 5 cm of bioretention filter materials (e.g. Søberg et al., 2017).”

• cites Søberg et al., 2017 sourceNot checked — no full text of the source

May combine two claims.

The complexity of metal adsorption increases with increases in the number of metals present due to competition between metals for binding sites, so different metals do not necessarily exhibit the same behavior under identical conditions.

“These findings illustrate that the complexity of metal adsorption increases with increases in the number of metals present due to competition between metals for binding sites, so different metals do not necessarily exhibit the same behavior under identical conditions (Bradl, 2004).”

• cites Bradl, 2004 sourceNot checked — no full text of the source

May combine two claims.

With typical infiltration rates of <300 mm/h, contact times for a 600 mm deep filter are generally at least 2 h, although in practice the infiltration rate varies depending on material, filter depth, root macro pores, bioturbation, and clogging.

“With typical infiltration rates of <300 mm/h (FAWB, 2008; Hunt et al., 2012) contact times for a 600 mm deep filter are generally at least 2 h, although, in practice, the infiltration rate of course varies depending on the type of material, filter depth, root macro pores, bioturbation, and level of clogging.”

• cites FAWB, 2008Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Hunt et al., 2012 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Efficient removal indicates that metals are bound to the filter material in more stable forms than found in this study or that oxidation of organic matter did not occur.

“Efficient removal indicates that metals are bound to the filter material in more stable forms than found in this study or that oxidation of OM did not occur.”

May combine two claims.

The KB-OHIO material removed 68 and 83% of total Zn and Pb, respectively, in previous field-scale bioretention tests, but leached Ca, Cu, Fe, Mg and Mn.

“The KB-OHIO material removed 68 and 83% of total Zn and Pb, respectively, in previous field-scale bioretention tests, but leached Ca, Cu, Fe, Mg and Mn (Winston et al. 2015).”

• cites Winston et al. 2015Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

May combine two claims.

Cr(III) is rapidly adsorbed by soil, specifically by Fe and Mn oxides, having particularly high affinities for Fe oxides; Cr adsorption increases with increases in pH and OM content, but decreases in the presence of competing cations, including ions of the other five metals considered.

“However, Cr(III) is rapidly adsorbed by soil, specifically by Fe and Mn oxides, having particularly high affinities for Fe oxides (Bradl, 2004). Furthermore, Cr adsorption increases with increases in pH and OM content, but decreases in the presence of competing cations, including ions of the other five metals considered here (Bradl, 2004).”

• cites Bradl, 2004 sourceNot checked — no full text of the source

May combine two claims.

At the highest initial concentrations, the metal concentrations exceeded the sorption capacity by far, so the percentage of metals adsorbed by LTU-TOP, NC-USA, DWA and Hekla-B was negligible and initial and final concentrations were approximately the same.

“These concentrations exceeded the metal sorption capacity by far. Thus, the percentage of the metals which was adsorbed by these materials was rather negligible and consequently initial and final concentrations were approximately the same.”

May combine two claims.

LTU-TOP efficiently removed metals in pilot-scale bioretention facilities under various ambient conditions, despite showing very low adsorption capacities in the present study.

“Although it showed very low adsorption capacities in the present study (Fig. 2), LTU-TOP efficiently removed metals in pilot-scale bioretention facilities under various ambient conditions (e.g. Blecken et al., 2009; Blecken et al., 2011; Søberg et al., 2017).”

• cites Blecken et al., 2009 sourceNot checked — no full text of the source
• cites Blecken et al., 2011 sourceNot checked — no full text of the source
• cites Søberg et al., 2017 sourceNot checked — no full text of the source

Classified as probably not a substantial claim. May combine two claims.

In physical adsorption, the bonds are relatively weak and easily break; metals may be adsorbed in several layers of molecules and easily desorbed by changes in temperature or other ambient water variables.

“In physical adsorption, the bonds are relatively weak and easily break (Bolis, 2013). Further, the metals may be adsorbed in several layers of molecules, and easily desorbed by changes in temperature or other ambient water variables (Bolis, 2013).”

• cites Bolis, 2013 sourceNot checked — no full text of the source

May combine two claims.

A major challenge when selecting bioretention filter materials is balancing high infiltration rates (but lower adsorption and contact time) offered by coarse materials, and potentially higher adsorption and longer contact time (but higher overflow) offered by finer materials.

“A major challenge when selecting bioretention filter materials is balancing high infiltration rates (but lower adsorption and contact time) offered by coarse materials, and potentially higher adsorption and longer contact time (but higher overflow) offered by finer materials.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

In recent years biochar has received considerable attention as a soil additive for heavy metal adsorption in stormwater treatment systems because it has various metal ion-binding functional groups and increases SSA due to its high porosity.

“In recent years biochar has received considerable attention as a soil additive for heavy metal adsorption in stormwater treatment systems because it has various metal ion-binding functional groups and increases SSA due to its high porosity (Mohanty et al., 2018).”

• cites Mohanty et al., 2018 sourceNot checked — no full text of the source

May combine two claims.

Addition of chalk may also help to improve metal adsorption by increasing the filter material's pH, while biochar addition seems to have no direct impact, despite increasing materials' SSA and OM contents.

“Addition of chalk may also help to improve metal adsorption by increasing the filter material’s pH, while biochar addition seems to have no direct impact, despite increasing materials’ SSA and OM contents.”

Probably not a substantial claim: may not pass S2 (checkable).

These partly conflicting results, in combination with findings of this study and previously reported effects of drying, clearly show that further analyses of metal fractionation in bioretention filter material are required.

“These partly conflicting results, in combination with findings of this study and previously reported effects of drying, clearly show that further analyses of metal fractionation in bioretention filter material are required.”

Classified as probably not a substantial claim. May combine two claims.

Chalk (calcium carbonate) contents of soils have been associated with metal fixation, and are considered important for metal adsorption and hence their soluble concentrations.

“Chalk (calcium carbonate) contents of soils have been associated with metal fixation, and are considered important for metal adsorption and hence their soluble concentrations (Alloway et al., 1988).”

• cites Alloway et al., 1988 sourceNot checked — no full text of the source

May combine two claims.

These observations are consistent with findings in the present study that most of the adsorbed metals were in the exchangeable (I), labile organic (II), and amorphous Fe- and Mn-oxides (III) fractions, where metals are easily desorbed by changes in ambient water ionic composition and under oxidizing conditions.

“These observations are consistent with findings in the present study that most of the adsorbed metals were in the exchangeable (I), labile organic (II), and amorphous Fe- and Mn-oxides (III) fractions (Fig. 4), where metals are easily desorbed by changes in ambient water ionic composition and under oxidizing conditions (Tessier et al., 1979).”

• cites Tessier et al., 1979 sourceNot checked — no full text of the source

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The high metal concentrations after extended dry periods may have been due to metal adsorption in potentially leachable forms, although the filter material was not subjected to confirmatory sequential extraction.

“This may have been due to metal adsorption in potentially leachable forms, although the filter material (similar to LTU-TOP) was not subjected to confirmatory sequential extraction.”

May combine two claims.

The relatively low SSA, low OM content, high D50 and high coefficient of uniformity of DWA-chalk are not favorable characteristics for metal adsorption; hence, its high pH (due to the chalk additive) is presumably the main characteristic that favors metal adsorption.

“The relatively low SSA, low OM content, high D50 and high coefficient of uniformity (Table 2) of DWA-chalk are not favorable characteristics for metal adsorption. Hence, its high pH (due to the chalk additive) is presumably the main characteristic that favors metal adsorption.”

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

Identifying the optimal mixture is challenging, especially as other objectives (e.g. supporting plants, treatment of other pollutants, and low cost) must also be met.

“Hence, identifying the optimal mixture is challenging, especially as other objectives (e.g. supporting plants, treatment of other pollutants, and low cost) must also be met.”

May combine two claims.

The Hasselfors material is coarser than the other materials and is likely to provide shorter retention times, and its metal adsorption rates may be lower than those observed in this study in practice.

“The Hasselfors material is coarser than the other materials (being based on gravel rather than sand; Fig. 1, Table 2). Thus, it is likely to provide shorter retention times than the other materials, and its metal adsorption rates may be lower than those observed in this study in practice.”

May combine two claims.

This has clear implications for the materials' long-term performance, during and after long dry periods and their disposal after maintenance.

“This has clear implications for the materials’ long-term performance, during and after long dry periods and their disposal after maintenance (when risks of metal desorption during excavation and movement of excavated filter material must be considered).”

Probably not a substantial claim: may not pass S4 (based).

Adding biochar may be undesirable due to its degradation over time.

“Moreover, adding it may be undesirable due to its degradation over time.”

Classified as probably not a substantial claim. May combine two claims.

Both chemisorption and physisorption of metals release heat, but the amounts of heat released differ substantially, in ranges of ca. 80-400 KJ/mol and 5-45 KJ/mol, respectively.

“Both chemisorption and physisorption of metals release heat, but the amounts of heat released differ substantially, in ranges of ca. 80–400 KJ/mol and 5–45 KJ/mol, respectively (Bolis, 2013).”

• cites Bolis, 2013 sourceNot checked — no full text of the source

May combine two claims.

Results of this study show that filter materials for stormwater bioretention have numerous differences and complex, sometimes conflicting characteristics, all of which may affect metal treatment.

“Results of this study show that filter materials for stormwater bioretention have numerous differences and complex, sometimes conflicting characteristics, all of which may affect metal treatment.”

Probably not a substantial claim: may not pass S3 (load-bearing).

A recent review of the utility of biochar as an additive in stormwater treatment systems concluded that it has varying capacity to remove metals.

“Accordingly, a recent review of the utility of biochar as an additive in stormwater treatment systems concluded that it has varying capacity to remove metals (Mohanty et al., 2018).”

• cites Mohanty et al., 2018 sourceNot checked — no full text of the source

May combine two claims.

The sediment trapped by stormwater bioretention systems will affect the metal fractionation as well as the filter material.

“Hence, the sediment trapped by stormwater bioretention systems will affect the metal fractionation as well as the filter material.”

May combine two claims.

The Orbicon material has much smaller particles than the other materials, which might pose risks for clogging and thus overflow or bypass.

“In contrast, the Orbicon material has much smaller particles than the other materials (Fig. 1, Table 2), which might pose risks for clogging and thus overflow or bypass.”

Classified as probably not a substantial claim.

Li and Davis (2008) found a close relationship between capture of metals and runoff particles.

“Furthermore, Li and Davis (2008) found a close relationship between capture of metals and runoff particles.”

• cites Li and Davis (2008) sourceNot checked — no full text of the source