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March 20, 2026 Get Citation Alerts Download PDF Add Note

Earl Parris, Jr. Individually, and on behalf of a Class of persons similarly situated v. 3M Company, et al.

District Court, N.D. Georgia

• Citations: None known
• Docket Number: 4:21-cv-00040

• Precedential Status: Unknown Status

• Opinion

• Authorities (16)

• Cited By (0)

• Summaries (0)

• Similar Cases (20.7K)

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Trial Court Document

IN THE UNITED STATES DISTRICT COURT

FOR THE NORTHERN DISTRICT OF GEORGIA

ROME DIVISION

EARL PARRIS, JR.

Individually, and on behalf of a Class of

persons similarly situated,

Plaintiff,

v. CIVIL ACTION FILE

NO. 4:21-CV-40-TWT

3M COMPANY, et al.,

Defendants.

OPINION AND ORDER

This is an action under the Clean Water Act. It is before the Court on
Defendants 3M Company, E.I. DuPont de Nemours, The Chemours Company,

and Daikin America, Inc.’s (“Daikin”) Motion to Exclude the Expert Testimony
of Jamie DeWitt [Doc. 880] and Motion for Leave to File Supplementary
Authority [Doc. 1068]. For the reasons set forth below, the Court GRANTS in
part and DENIES in part the Defendants’ Motion to Exclude the
Expert Testimony of Jamie DeWitt [Doc. 880] and GRANTS their Motion for
Leave to File Supplementary Authority [Doc. 1068].

                 I.  Background                                   

This case arises out of the contamination of surface waters and drinking
water in Chattooga County, Georgia, with per- and polyfluoroalkyl substances
known as “PFAS.” (2d Am. Compl. ¶ 1 [Doc. 280].) The facts of this case are
well known to the parties by this point, so the Court will not belabor them here.
In essence, Plaintiff Earl Parris, Jr., alleges that the Defendants have
contaminated his city’s water supply and thus his household water with PFAS.

Parris is a resident of Summerville, Georgia, who receives running, potable
water to his home from the Summerville Public Works and Utilities
Department. ( ¶ 21.) The City of Summerville, which has intervened in this
case, uses Raccoon Creek as the main source of its municipal water supply.
( ) The Court will collectively refer to Plaintiff Parris and Intervenor-Plaintiff
Summerville as the Plaintiffs. The Defendants are the following companies,
which allegedly manufactured and supplied the PFAS discharged into Raccoon

Creek: 3M Company, Daikin America, Inc., E.I. du Pont de Nemours and

Company, and The Chemours Company. At present, the Defendants jointly

move to exclude the expert witness testimony of Jamie DeWitt and move for
leave to file supplementary authority regarding their motion to exclude.
II. Legal Standard

Federal Rule of Evidence 702 governs the admissibility of expert

testimony. Under that rule, “expert testimony is admissible if (1) the expert is
qualified to testify regarding the subject of the testimony; (2) the expert’s
methodology is sufficiently reliable as determined by the sort of inquiry
mandated in ; and (3) the expert’s testimony will assist the trier of fact
in understanding the evidence or determining a fact at issue.”

2

, 766 F.3d 1296, 1304 (11th Cir. 2014) (citation
modified). Courts perform a “gatekeeping role” in excluding expert testimony
that does not satisfy these qualification, reliability, and helpfulness

requirements. , 509 U.S. 579, 597 (1993).

“This gatekeeping role, however, is not intended to supplant the adversary
system or the role of the jury” in determining the persuasiveness of an expert’s
testimony. , 730 F.3d 1278, 1282 (11th Cir.

2013) (citation modified). Rather, the goal is to “make certain that an expert
. . . employs in the courtroom the same level of intellectual rigor that
characterizes the practice of an expert in the relevant field.”

, [387 F.3d 1244, 1260](https://www.courtlistener.com/opinion/76761/united-states-v-richard-junior-frazier/#1260) (11th Cir. 2004) (en banc) (quoting         
         , [526 U.S. 137, 152](https://www.courtlistener.com/opinion/118271/kumho-tire-co-v-carmichael/#152) (1999)). “The proponent of the expert 

testimony always bears the burden” of establishing qualification, reliability,
and helpfulness. (citation modified).

III. Discussion

Jamie DeWitt is a professor at Oregon State University in

environmental and molecular toxicology and holds a Ph.D. in environmental
science and neural science. (Defs.’ Mot. to Exclude DeWitt, Ex. 1 (“DeWitt
Report”), 1 at 58 [Doc. 880-1].) She has co-authored twenty-one primary
research articles on PFAS toxicity as well as other publications, and she has

1 The pagination of this exhibit reflects the PDF pagination.

3

held a number of positions with government agencies and groups related to
PFAS exposure and toxicology. ( at 8–11.) Based on her assessment of the
available scientific literature, DeWitt opines that “exposure to PFAS poses

substantial present or potential hazard to human health” and goes on to opine
on the ways in which PFAS exposure is associated with adverse health effects
in humans. ( at 13.)

The Defendants challenge DeWitt’s testimony on three grounds:
qualification, relevance, and reliability. The Court addresses each of these
grounds below. Before doing so, the Court notes that it grants the Defendants’
Motion for Leave to File Supplemental Authority, which contains a copy of an

opinion in , 805 F.Supp.3d 626 (E.D.N.C. 2025),

and , Case

Nos. 7:17-CV-195 & 7:17-CV-209 (E.D.N.C. Dec. 17, 2025).

A. Qualification

Rule 702 provides that a witness may be “qualified as an expert by
knowledge, skill, experience, training, or education.” Fed. R. Evid. 702. When

assessing a witness’s qualifications, the district court must focus on “the
matter to which the expert seeks to testify—i.e., ‘to the task at hand.’”
, 995 F.3d 839, 854 (11th Cir. 2021) (quoting , 509 U.S. at 597). While a witness may be “well-trained, highly educated, and
experienced” with an “impressive professional track record,” Rule 702
4

contemplates “a more thorough analysis of whether [the witness] is qualified
and competent to testify as an expert

.” , 239 F. Supp. 2d 1308, 1316 (N.D. Ga.

2002) (emphasis added). “It is for that reason that ‘expertise in one field does
not qualify a witness to testify about others.’” , 995 F.3d at 854 (quoting
, 772 F.3d 1352, 1368 (11th Cir.

2014)). The question whether a proposed witness is qualified to testify as an
expert rests within the district court’s discretion. , 239 F. Supp. 2dat 1314
(citing , 528 F.2d 987, 990 (5th Cir.

1976)).

The Defendants’ first qualification challenge is that DeWitt is a
toxicologist trained to study only animals and not an epidemiologist trained to
study humans. (Defs.’ Mot. to Exclude DeWitt, at 3–5). The Defendants
additionally contend that DeWitt is not qualified to rebut Daikin’s expert
Anders Abelmann because Abelmann is an industrial hygienist opining on the
ways humans can be exposed to PFAS while DeWitt is a toxicologist untrained

in the kind of “human exposure assessments” considered by Abelmann. ( at
6–7.)

The Court disagrees on both fronts. The Defendants’ qualification
challenge is not well taken. First, DeWitt is qualified to testify about the
adverse human health hazards engendered by exposure to PFAS, including the
5

types of PFAS (PFOA and PFOS2) at issue in this case. DeWitt is a recognized
PFAS expert and has established her career studying and reviewing literature
on the potential human health effects of PFAS exposure. She has “co-

authorized 21 review articles/commentaries on PFAS toxicity and use, two
book chapters related to PFAS immunotoxicity, and edited one of the first
comprehensive texts on the toxicity of PFAS.” (DeWitt Report, at 11.) She has
also been nominated to or tasked with a variety of PFAS-related roles,
including as a member of the EPA’s 2021–22 PFAS Science Advisory Board, a
member of an International Agency for Research on Cancer working group

studying “carcinogenicity of PFOA,” a reviewer for the U.S. National

Toxicology Program’s publication on the “immunotoxicity of PFOA and PFOS,”
a “Community Liaison” to a committee charged by the Centers for Disease
Control and Prevention and the National Institute of Environmental Health
Sciences with “examin[ing] health outcomes associated with the most widely
studied PFAS,” a witness testifying before three subcommittees of the U.S.
House of Representatives on PFAS toxicity, an external peer reviewer for the

EPA’s “health effect documents for PFOA and PFOS in 2014,” an external

reviewer for the U.S. Agency for Toxic Substances and Disease Registry’s
“Toxicological Profile for PFAS in 2017” and other PFAS documents, and a

2 PFOS is short for perfluorooctanesulfonic acid, and PFOA is short for
perfluorooctanoic acid.

6

PFAS advisor for governmental agencies in Michigan, North Carolina, and
Tennessee. ( at 9–10.) She is therefore “qualified and competent to testify as
an expert as to the subject matter of [her] proposed testimony.” , [239

F. Supp. 2d at 1316](https://www.courtlistener.com/opinion/2412538/jack-v-glaxo-wellcome-inc/#1316).

These credentials make DeWitt qualified to evaluate studies and data
on PFAS toxicity, including both toxicological and epidemiological data. While
DeWitt is trained as a toxicologist and not an epidemiologist, that is of no
difference here. DeWitt has testified to the Court’s satisfaction that she has
previously assessed epidemiological studies and can properly do so here,
including for bias, cofounding, and other flaws. (Pls.’ Resp. Br. in Opp’n to

Defs.’ Mot. to Exclude DeWitt, Ex. 2 (“Pls.’ DeWitt Dep. Excerpt”), at 138:17–
139:10, 141:1–13 [Doc. 955-2].)

Second, DeWitt is adequately qualified to rebut Daikin’s expert
Abelmann. DeWitt identifies three issues with Abelmann’s report: (1) he
misinterpreted one study by relying on it as an indicator of “absolute levels of
exposure” for various exposure pathways, (2) he misinterpreted another study

by relying on it to identify food as the dominant PFAS exposure pathway in
Summerville, and (3) he failed to “include any data on PFOA levels in food in
Summerville.” (Defs.’ Mot. to Exclude DeWitt, Ex. 8, at 17–18.) DeWitt is an
experienced scientist qualified to review and interpret the kinds of scientific
literature on which Abelmann relies. She has not stretched beyond her
7

credentials by identifying how Abelmann may have misinterpreted existing
studies or identifying a fundamental flaw in his conclusions.

B. Relevance

An expert’s opinions must be helpful to a trier of fact. Fed. R.
Evid. 702(a). The helpfulness of an expert’s opinions to a trier of fact speaks
“primarily to relevance,” which is a “liberal” standard.

, 813 F.3d 983, 988 (11th Cir. 2016) (citations omitted). “Expert
testimony which does not relate to any issue in the case is not relevant and,
ergo, non-helpful.” , 509 U.S. at 591 (citation omitted). The Defendants
ask this Court to exclude DeWitt’s testimony on PFAS other than PFOS and

PFOA. (Defs.’ Mot. to Exclude DeWitt, at 21.) They argue that other types of
PFAS “are not at issue in this case.” ( at 3.)

Given the liberal relevance standard, the Court declines to exclude
DeWitt’s testimony referring to PFAS other than PFOS or PFOA. Testimony
on the risks of PFAS generally, including but not limited to PFOS and PFOA,
is relevant to this litigation. According to the Complaint, the Defendants

contaminated the Raccoon Creek watershed with PFAS “including” PFOS and
PFOA, and sampling data revealed PFOS, PFOA, and other PFAS substances

in Raccoon Creek. (See, e.g., 2d Am. Compl. ¶¶ 88–90.) The Complaint also
alleges that the Defendants manufactured PFAS other than PFOS and PFOA

and were aware of the danger presented by PFAS chemicals as a whole. (

8

, ¶ 81–82.) Moreover, other expert witnesses appear to have identified
PFAS other than PFOS and PFOA in Summerville’s water supply. ( ,

Defs.’ Mot. to Exclude Davis, Ex. 8, at 31–34.) The risks posed by PFAS

substances other than PFOS and PFOA would therefore be helpful to a trier of
fact.

C. Reliability

In determining whether an expert witness’s testimony is reliable under
Rule 702, the Court must evaluate “whether the reasoning or methodology
underlying the testimony is scientifically valid and . . . whether that reasoning
or methodology properly can be applied to the facts in issue.” , 509 U.S.

at 592–93. sets forth a number of factors relevant to this inquiry,
including (1) whether an expert’s theory or technique can be tested;
(2) whether the theory or technique has been subjected to peer review and
publication; (3) the known or potential rate of error of a scientific technique;
and (4) whether a known technique has achieved widespread acceptance in the
scientific community. at 593–94. These factors are not intended to be a

“definitive checklist,” at 593; rather, “the law grants the trial judge broad
latitude to determine . . . whether ’s specific factors are, or are not,
reasonable measures of reliability in a particular case.” , 526 U.S. at 153.

The Eleventh Circuit has further recognized the necessity of a “flexible,
9

context-sensitive application of ” especially in cases where the
reliability of an expert’s opinion may turn more on the expert’s competency
than his methodology. , 760 F.3d 1322, 1340 (11th

Cir. 2014) (Garza, J., concurring). Thus, “there are instances in which a district
court may determine the reliability prong under based primarily upon

an expert’s experience and general knowledge in the field.”

, 613 F.3d 1329, 1336 (11th Cir. 2010). Still, “the qualifications and
reliability prongs of are conceptually distinct inquiries that district
courts may not collapse into each other.” , 995

F.3d 839, 853 (11th Cir. 2021); , 760 F.3d at 1330 n.13 (quoting

  , [613 F.3d at 1336](https://www.courtlistener.com/opinion/152948/douglas-c-kilpatrick-v-breg-inc/#1336)).                                            

Ultimately, the district court’s objective under is to “make

certain that an expert . . . employs in the courtroom the same level of
intellectual rigor that characterizes the practice of an expert in the relevant
field.” , 526 U.S. at 152. To this end, a district court may not admit
opinions that “[are] connected to existing data only by the of the

expert” or leave “too great an analytical gap between the data and the opinion
proffered.” , 522 U.S. 136, 146 (1997).

The Defendants challenge the reliability of DeWitt’s testimony from five
angles. They contend that her testimony fails to (1) establish general
causation; (2) establish that there is no safe level of PFAS exposure; (3) justify
10

the applicability of animal studies to humans; (4) make transparent her
methodology such that it is reproduceable; and (5) justify opinions on PFAS
other than PFOS and PFOA.

1. General Causation and Risk Assessment
   The Defendants contend that DeWitt’s testimony is unreliable because it fails to adequately consider the “three sources of evidence relevant to general causation.” (Defs.’ Mot. to Exclude DeWitt, at 11.) Those three sources are “epidemiological evidence, the dose-response relationship, and the background risk of disease.” (Defs.’ Mot. to Exclude DeWitt, at 11 (citing
   , 119 F.4th 937, 941 (11th Cir. 2024).)
   

The Plaintiffs respond that DeWitt’s testimony does not seek to prove
general (or specific) causation as would be required in a toxic tort case
connecting a given pollutant to particular personal injuries. Instead, they
argue that the testimony reflects a public health “risk assessment” that
assesses the weight of the scientific evidence to identify the risks associated
with PFAS exposure. (Pls.’ Resp. Br. in Opp’n to Defs.’ Mot. to Exclude, at 14–
15 [Doc. 955].) The Plaintiffs contend that the goal of the testimony is to

explain to a jury why a city like Summerville might choose to abate the threat
of PFAS in its water supply.

The Court holds that DeWitt’s assessment of risk is reliable for the
purpose of contextualizing the damages claimed by the Plaintiffs, though not
11

reliable for establishing specific or general causation. The Eleventh Court in
, 401 F.3d 1233 (11th Cir. 2005),

distinguished between causation evidence and risk assessment evidence. at

1. According to , a risk assessment evaluates whether the potential risks of a substance outweigh the potential benefits, whereas a causation analysis evaluates whether a substance more likely than not causes or caused an alleged harm. , 401 F.3d at 1249. Because was a toxic
   tort action involving alleged personal injuries, the Eleventh Circuit found that it “[o]bviously . . . must focus on assessing causation, not a cost-benefit analysis.” It further noted that a risk assessment would not be reliable

evidence of legal causation under . at 1250. Relying on ,

, 119 F.4th 937, 941 (11th Cir. 2024),

affirmed the exclusion of testimony by the plaintiffs’ general causation expert
in a similar toxic tort action for personal injury damages. at 945–46.
held that the district court did not abuse its discretion
when it excluded an expert’s testimony for failing to “identify a ‘toxin’ and

prove it ‘[was] harmful above a particular threshold.’” (referring to the dose-
response relationship).

Here, the Plaintiffs do not seek to prove—and need not prove—legal
causation between PFAS and any particular health injuries. The Plaintiffs
instead seek to rely on DeWitt’s expert testimony to support Summerville’s
12

decision to build a treatment system to remove PFAS from its water supply
and take other abatement measures—the alleged damages in this case. DeWitt
testified that, while her report discusses the association between PFAS and

various adverse health outcomes, it does not assert a “cause and effect”
relationship. (Pls.’ DeWitt Dep. Excerpt, at 126:5–9.) She further testified that
she “do[es] not intend to offer any causality opinions,” ( at 159:23–24), as she
was merely asked to “evaluate the existing toxicological data on PFAS and
determine the toxicological hazards,” ( at 127:11–13; at 158:5–10

(testifying to the same)).

Therefore, the Defendants’ arguments that DeWitt’s testimony does not

amount to reliable general causation evidence are largely immaterial.
Although association and causation are related, the concepts are not
equivalent. Thus, it is possible for an expert to assess whether the weight of
the scientific evidence supports an association between PFAS and a particular
adverse health without opining on causation. Such may be relevant when a
government agency must assess the available evidence and choose whether to

take precautionary regulatory action in response to exposure to a chemical.3
That is the case here with Summerville. Where an expert does seek to establish
general causation, the Defendants are correct that the Eleventh Circuit has

3 For the same reason, DeWitt’s testimony about the precautionary

principle is relevant and not made unreliable by the requirements of proving
causation.

13

looked favorably on testimony that applies the “Bradford Hill” factors to
individual studies, assesses the dose-response relationship, and assesses
background risk. , 119 F.4th at 941. But, as explained,

DeWitt’s testimony need not satisfy the standard for proving general

causation. It need only satisfy for what it sets out to do—identifying
potential health risks associated with PFAS exposure in the scientific
literature. For the reasons explained elsewhere below, it does so.

2. No Safe Exposure Level

To the extent DeWitt’s testimony contains an opinion that the only safe
level of PFAS exposure is zero, the Court excludes that opinion. The

Defendants point out that DeWitt offered an opinion about no level of PFAS
exposure being safe, citing the following sentence in her report: “The U.S.
EPA’s established [maximum contaminant level goals of zero] for PFOA and
PFOS and the evidence upon which the actions were based[ ] support my

opinion that the weight of the evidence is that PFAS exposure through
contaminated drinking water is a risk for cancer and that level of PFOA or

PFOS in drinking water can be considered ‘safe’ with respect to cancer risks.”4

4 The Defendants also point to DeWitt’s rebuttal deposition in which she
apparently testified “no level of exposure to PFOA or PFOS is without risk and
specifically carcinogenic risk.” (Reply Br. in Supp. of Defs.’ Mot. to File Suppl.
Auth., at 2.) The Court cannot identify this testimony in the record at this time,
however. The Defendants’ other citations to DeWitt’s testimony refer to
regulatory goals, which are distinct from testimony of safe PFAS exposure
levels. Additionally, the Court is aware of deposition testimony in which
14

(DeWitt Report, at 20; at 19 (regarding MCLGs of 0 ppt).) As the

Defendants explain, determining particular “safe” and “unsafe” levels of PFAS
is not supported by DeWitt’s existing testimony. Determining such exposure

levels requires establishing a causal link between PFAS and known adverse
health effects, including by evaluating such factors as the dose-response
relationship. , 119 F.4th 937, 945–

46 (11th Cir. 2024) (affirming a district court order excluding an expert’s
causation testimony for failing to “prove” an alleged toxin “[was] harmful above
a particular threshold”).

The Court agrees with courts in other districts that have excluded

DeWitt’s testimony for failure to bridge the gap between her risk assessment
and her opinion on unsafe PFAS levels. In , a North Carolina district court
excluded DeWitt’s testimony as unhelpful to a jury in determining whether
PFAS interfered with the plaintiffs’ use and enjoyment of their property. 805
F. Supp. 3d at 656. It reasoned that DeWitt leaped without support to the
conclusion that “any non-zero level of PFAS in drinking water is unsafe” and

could therefore only opine on adverse health risks associated with PFAS
exposure, which the court did not find helpful to a jury on the questions of

DeWitt is asked what an “acceptable level” of PFAS exposure would be and
responds by deferring to the acceptable levels prescribed by the EPA, which for
PFOS and PFOA are 0 ppt for the maximum contaminant level goal and 4 ppt
for the maximum containment level. (Defs.’ Mot. to Exclude DeWitt, Ex. 3, at
143:1–14 [Doc. 880-3].)

15

specific or general causation. In , the same judge relied on to

exclude DeWitt’s testimony for the same reason. , Case Nos. 7:17-

CV-195 & 7:17-CV-209, at 40–41. Like her risk assessment in and

, DeWitt’s risk assessment here has not done enough to establish specific
safe and unsafe PFAS exposure levels. That being said, the Court notes that
and differ from this case in that the Court finds DeWitt’s
assessment of risk helpful to a jury on the question of the Plaintiffs’ requested
damages—the necessity and cost of Summerville’s PFAS abatement measures.

3. Extrapolation of Animal Studies to Humans

The Defendants contend that DeWitt “improperly extrapolated from

results of animal studies to assert that PFAS causes human health effects.”
(Defs.’ Mot. to Exclude DeWitt, at 19.) They cite

, 131 F. Supp. 2d 1347 (N.D. Ga. 2001), for the
proposition that “[e]xtrapolations from animal studies to human beings
generally are not considered reliable in the absence of a credible scientific
explanation of why such extrapolation is warranted.” ( (quoting , 131 F. Supp. 2d at 1366).)

The Court finds DeWitt’s testimony reliable to the extent its conclusions
on human health consequences are supported by studies on animals. DeWitt
sufficiently bridges the analytical gap between PFAS studies involving
animals and the application of those studies to humans. First, her report notes
16

that “experimental animal models . . . are accepted models for human health
in the toxicological sciences as well as other biomedical sciences.” (DeWitt
Report, at 28.) It continues: “While humans and animals are not exactly alike,

evaluation of toxicity of chemicals in experimental animal models is a
cornerstone of human safety evaluation, and findings in animal toxicology
studies are applicable to humans.” ( at 25; (“Data from both

[toxicological and epidemiological] studies are [ ] used to reach conclusions
about the likelihood of adverse effects following exposure to an exogenous
agent.”). The necessity of animal studies is evident to the Court, as it would be
“unethical to test potentially toxic substances on humans.” (Pls.’ Resp. Br. in

Opp’n to Defs.’ Mot. to Exclude DeWitt, at 18.)

Second, in the context of PFAS animal studies in particular, DeWitt
explains why she found studies of animals applicable to humans. She states
that the results of prior animal studies are “highly relevant to human health”
because “adverse health outcomes [were] observed in experimental animal
studies

                                               and                
                          .” (   DeWitt Report, at 28.) She       

further explains in her report that toxicologists “frequently rely on
experimental animal models . . . to understand adverse health outcomes from
chemical exposures . . . in humans.” ( at 25.) Contrary to the Defendants’
17

position, DeWitt has presented “a credible scientific explanation of why such
extrapolation is warranted.” , 131 F. Supp. 2d at 1366. At bottom,

nothing about DeWitt’s testimony suggests that she is “employing in the

courtroom” anything other than the “same level of rigor that characterizes the
practice of an expert” in her field. , 526 U.S. at 152.

4. Reproducibility

The Defendants take issue with the reproducibility of DeWitt’s
methodology. (Reply Br. in Supp. of Defs.’ Mot. to Exclude DeWitt, at 11
[Doc. 1011].) They argue that her weight-of-the-evidence methodology is not
“transparent, testable, [or] reproducible,” as she does not expressly assign

weight to any evidence or explain similar balancing decisions.

The Court finds DeWitt’s weight-of-the-evidence methodology

adequately reproduceable for purposes. DeWitt explains her weight-

of-the-evidence approach in the following manner: She first “identif[ied]
existing narrative reviews, systematic reviews, meta-analyses, health risk
assessments, and scientific opinions related to PFAS health effects conducted

by national and international government agencies and/or entities.” (DeWitt
Report, at 15.) She identified other literature as well using “targeted online
searches of online databases, including PubMed, Google Scholar, and
PubChem” and using specified search terms, then narrowed her review to

results that matched certain specified criteria. ( .) She then categorized that
18

literature by quality (e.g., high, medium, or low) and type of review (e.g.,
systematic reviews and meta-analyses published by national and international
government agencies and/or entities, the same published in peer-reviewed

scientific literature, primary research articles published in peer-reviewed
scientific literature, and other sources). ( at 16–17.) Lastly, she “appraise[d]”
the literature in those groups to come to her ultimate conclusions. ( at 17.)
While DeWitt’s explanation for how she “appraised” each study or group
of studies may be light on details, her explanation of her process is sufficient.
Moreover, Dewitt testified that other toxicologists and scientists conduct
literature reviews as a “routine part” of their job, and she noted that she has

been asked to conduct similar reviews as an expert in her field while working
for reputable governmental agencies and entities. (Pls.’ DeWitt Dep. Excerpt,
at 161:16–25; DeWitt Report, at 9–10.) If the goal is to “make certain that
an expert . . . employs in the courtroom the same level of intellectual rigor that
characterizes the practice of an expert in the relevant field,” such can be said
in this case. , 526 U.S. at 152. The Court sees no reason why

another expert could not conduct a similar weight-of-the-evidence assessment
and come to the same or a different conclusion. Lastly, the Court notes that
other courts have found weight-of-the-evidence analyses reliable and
admissible. , , 2009 WL 3806435, at

*5–6 (M.D. Fla. June 23, 2009) (holding that an expert’s weight-of-the-evidence
19

methodology was “a reliable process for gathering and assessing the scientific
evidence”); , 858 F.3d

787, 795 (3d Cir. 2017) (noting that “weight of the evidence” methodologies are

“generally reliable,” though “each application is distinct and should be
analyzed for reliability”); 639

F.3d 11, 18 (1st Cir. 2011)(“The fact that the role of judgment in the weight of
the evidence approach is more readily apparent than it is in other
methodologies does not mean that the approach is any less scientific.”).
5. PFAS Other Than PFOS and PFOA

The Defendants seek to exclude DeWitt’s opinions on PFAS other than

PFOS and PFOA as unreliable. They argue that DeWitt presumes without

sufficient evidentiary support that “all PFAS are alike in human causality.”
(Defs.’ Mot. to Exclude DeWitt, at 23.) And they further argue that “nearly all
of the studies” cited by DeWitt concern only PFOS or PFOA, making it difficult
to draw conclusions about the other thousands of chemicals that fall under the
category of PFAS. (Id. at 21–22.)

The Court disagrees with the Defendants and finds DeWitt’s testimony
sufficiently reliable to the extent it opines on PFOS and PFOA, the four other
“well-studied” PFAS compounds identified (PFHxS, PFBS, PFNA, and HFPO-

DA), and other PFAS more generally. Here, the Defendants merely point out
that DeWitt opines on both well-studied and less-studied PFAS, but DeWitt’s
20

testimony explaining why she has opined on both is sufficient. First, her most
of her opinions are expressly confined to PFOS, PFOA, or the four other “well-
studied” PFAS. (See DeWitt Report, at 13.) To the extent she opines on PFAS
generally, including both well-studied and less-studied PFAS, DeWitt testified
that the relatively “understudied” PFAS “are part of the same class of
chemicals,” “share similar physical-chemical characteristics,” and likely have
the same health risks due to key consistencies across all available PFAS data.
(Id, at 14, 28.)
IV. Conclusion
For the reasons set forth above, the Court GRANTS in part and DENIES
in part Defendants 3M Company, E.I. DuPont de Nemours, The Chemours
Company, and Daikin America, Inc.’s Motion to Exclude the Expert Testimony
of Jamie DeWitt [Doc. 880]. The Motion is granted as to Jamie DeWitt’s
testimony that the only safe level of PFAS exposure is zero and denied as to all
other relief requested therein. Additionally, the Court GRANTS their Motion
for Leave to File Supplementary Authority [Doc. 1068].
SO ORDERED, this 20th day of March, 2026.

                                    THOMAS W. THRASH, JR. 
                                    United States District Judge 

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