A Retrospective Chart Review Evaluating the Relationship between Cancer Diagnosis and Residential Water Source on the Lower Eastern Shore of Maryland, USA

Abstract

Well water contamination in heavily agricultural regions has previously been linked with increased cancer incidence and mortality. The lower Eastern shore of Maryland is a rural, agricultural region with some of the highest rates of cancer in Maryland and the United States. Our study sought to characterize residential private well water use among cancer patients on the lower Eastern shore of Maryland, and to compare private well water utilization between cancer patients and the general regional population. Retrospective chart review was conducted to identify patients diagnosed with colon, lung, melanoma or breast cancer at a regional hospital from 1 January 2017 through 31 December 2018. Residential water source was determined using residential address and municipal water records. Fisher’s exact test was used to compare residential private well water utilization between our study population and the baseline regional population. The majority of cancer patients (57%) lived in homes supplied by private well water (428/746). Cancer patients were more likely to live in homes supplied by private well water compared to individuals in the general regional population (57% vs. 32%, p < 0.001). In conclusion, cancer patients on the lower Eastern shore of Maryland were more likely to live in homes supplied by residential private well water than the regional population. Additional studies are needed to evaluate well water use and cancer risk in this vulnerable region.

Full text

International Journal of
Environmental Research
and Public Health
Article
A Retrospective Chart Review Evaluating the Relationship
between Cancer Diagnosis and Residential Water Source on the
Lower Eastern Shore of Maryland, USA
Angela DeRidder 1, * , Sowjanya Kalluri 2and Veera Holdai 3


Citation: DeRidder, A.; Kalluri, S.;
Holdai, V. A Retrospective Chart
Review Evaluating the Relationship
between Cancer Diagnosis and
Residential Water Source on the
Lower Eastern Shore of Maryland,
USA. Int. J. Environ. Res. Public Health
2021,18, 145. https://doi.org/
10.3390/ijerph18010145
Received: 9 November 2020
Accepted: 26 December 2020
Published: 28 December 2020
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional claims
in published maps and institutional
affiliations.
Copyright: © 2020 by the authors. Li-
censeeMDPI, Basel, Switzerland. This
articleis an open accessarticle distributed
under the terms and conditions of the
Creative CommonsAttribution(CC BY)
license(https://creativecommons.org/
licenses/by/4.0/).
1Department of Hematology and Oncology, TidalHealth Peninsula Regional, 100 E. Carroll St.,
Salisbury, MD 21801, USA
2Department of Internal Medicine, TidalHealth Peninsula Regional, 100 E. Carroll St.,
Salisbury, MD 21801, USA; sowjanyakalluri2@gmail.com
3Department of Math and Computer Science, Salisbury University, 1101 Camden Ave,
Salisbury, MD 21801, USA; VXholdai@salisbury.edu
*Correspondence: angela.deridder@peninsula.org; Tel.: +1-410-749-1282; Fax: +1-410-749-7821
Abstract:
Well water contamination in heavily agricultural regions has previously been linked with
increased cancer incidence and mortality. The lower Eastern shore of Maryland is a rural, agricultural
region with some of the highest rates of cancer in Maryland and the United States. Our study
sought to characterize residential private well water use among cancer patients on the lower Eastern
shore of Maryland, and to compare private well water utilization between cancer patients and the
general regional population. Retrospective chart review was conducted to identify patients diagnosed
with colon, lung, melanoma or breast cancer at a regional hospital from 1 January 2017 through
31 December 2018. Residential water source was determined using residential address and municipal
water records. Fisher’s exact test was used to compare residential private well water utilization
between our study population and the baseline regional population. The majority of cancer patients
(57%) lived in homes supplied by private well water (428/746). Cancer patients were more likely
to live in homes supplied by private well water compared to individuals in the general regional
population (57% vs. 32%, p< 0.001). In conclusion, cancer patients on the lower Eastern shore of
Maryland were more likely to live in homes supplied by residential private well water than the
regional population. Additional studies are needed to evaluate well water use and cancer risk in this
vulnerable region.
Keywords:
drinking water; groundwater contamination; cancer risk; rural health; agricultural pollution
1. Introduction
Per the Environmental Protection Agency (EPA), it is estimated that more than 13 mil-
lion households rely on private wells for drinking water in the United States (U.S.) [
1
].
However, drinking water from private wells can pose potential health hazards. The EPA
does not regulate private wells, and routine testing of private wells is voluntary and per
the owner’s discretion [
2
]. Private well owners are therefore responsible for the safety of
their own water supply.
As of 2018, the EPA recommends testing private wells annually for coliform bacteria,
nitrates, total dissolved solids, and pH levels [
2
]. In addition, well owners should determine
whether ground water supplying their private well is under direct influence from surface
water. Substances such as nitrates/nitrites, arsenic, and organic chemicals can contaminate
private wells through groundwater movement and surface water runoff [
3
]. Also known
as non-point source pollution, surface water runoff is particularly concerning in heavily
agricultural regions. Due to the common use of fertilizers and pesticides/herbicides, and
the presence of animal waste and by-products, agricultural non-point source pollution is a
leading cause of impaired water quality and ground water contamination in the U.S. [
4
,
5
].
Int. J. Environ. Res. Public Health 2021,18, 145. https://doi.org/10.3390/ijerph18010145 https://www.mdpi.com/journal/ijerph

Int. J. Environ. Res. Public Health 2021,18, 145 2 of 13
Ground water contamination from agricultural sources can adversely affect human
health in multiple ways. Elevated arsenic exposure in drinking water is associated with
increased risk of skin, lung and bladder cancer [
6
,
7
]. Similarly, long term-exposure to
nitrites and nitrates in drinking water has been associated with increased risk of colon
cancer and breast cancer in certain patient populations [
8
–
10
]. Organic chemicals have
been linked to a number of adverse effects on human health, including breast cancer [
11
].
While these contaminants can come from naturally occurring sources, such as arsenic
deposits and wildlife waste products, studies have also shown that these potentially
carcinogenic contaminants are found in a number of common agricultural byproducts
and applications [
12
,
13
]. Rural, agricultural regions may therefore be at higher risk for
groundwater contamination and its potential health implications.
The lower Eastern shore of Maryland lies on the east side of the Chesapeake Bay and
consists of Wicomico, Worcester and Somerset counties (Figure 1). The main economic
activities for this rural region include agriculture and large-scale chicken breeding. In
2014, Maryland ranked ninth among all states in the nation in broiler chicken production,
with Wicomico, Worcester and Somerset counties being the top three producers of poultry
and eggs within the state [
14
–
17
]. Approximately 600 million chickens are produced
yearly between the lower Eastern shore of Maryland and the nearby county of Sussex,
Delaware [
18
]. Per the EPA, these birds produce approximately 5.7 billion pounds of
manure annually, contributing around 5 million pounds of nitrogen to local waterways per
year. Combined with other agricultural sources on the lower Eastern shore, these farms,
also known as animal feeding operations (AFOs), add a total of 119 million pounds of
nitrogen pollution to the Chesapeake Bay on an annual basis. Given this documented
contamination of local waterways by agricultural non-point source pollution, the economic
activities prevalent on the lower Eastern shore of Maryland raise concern over the risk for
ground water contamination in this region.
Int. J. Environ. Res. Public Health 2021, 18, x 2 of 13
in heavily agricultural regions. Due to the common use of fertilizers and pesticides/herb-
icides, and the presence of animal waste and by-products, agricultural non-point source
pollution is a leading cause of impaired water quality and ground water contamination
in the U.S. [4,5].
Ground water contamination from agricultural sources can adversely affect human
health in multiple ways. Elevated arsenic exposure in drinking water is associated with
increased risk of skin, lung and bladder cancer [6,7]. Similarly, long term-exposure to ni-
trites and nitrates in drinking water has been associated with increased risk of colon can-
cer and breast cancer in certain patient populations [8–10]. Organic chemicals have been
linked to a number of adverse effects on human health, including breast cancer [11]. While
these contaminants can come from naturally occurring sources, such as arsenic deposits
and wildlife waste products, studies have also shown that these potentially carcinogenic
contaminants are found in a number of common agricultural byproducts and applications
[12,13]. Rural, agricultural regions may therefore be at higher risk for groundwater con-
tamination and its potential health implications.
The lower Eastern shore of Maryland lies on the east side of the Chesapeake Bay and
consists of Wicomico, Worcester and Somerset counties (Figure 1). The main economic
activities for this rural region include agriculture and large-scale chicken breeding. In
2014, Maryland ranked ninth among all states in the nation in broiler chicken production,
with Wicomico, Worcester and Somerset counties being the top three producers of poultry
and eggs within the state [14–17]. Approximately 600 million chickens are produced
yearly between the lower Eastern shore of Maryland and the nearby county of Sussex,
Delaware [18]. Per the EPA, these birds produce approximately 5.7 billion pounds of ma-
nure annually, contributing around 5 million pounds of nitrogen to local waterways per
year. Combined with other agricultural sources on the lower Eastern shore, these farms,
also known as animal feeding operations (AFOs), add a total of 119 million pounds of
nitrogen pollution to the Chesapeake Bay on an annual basis. Given this documented con-
tamination of local waterways by agricultural non-point source pollution, the economic
activities prevalent on the lower Eastern shore of Maryland raise concern over the risk for
ground water contamination in this region.
Figure 1. The lower Eastern shore of Maryland, U.S. Image created by MRamadhon and repro-
duced with permission.
Figure 1. The lower Eastern shore of Maryland, U.S. Image created by MRamadhon and reproduced with permission.
Local groundwater research suggests that these concerns may have merit. The U.S.
Geological Survey (USGS) National Water-Quality Assessment Program measured concen-
trations of pesticides and herbicides in samples collected from 2001 to 2004 from 47 wells in
Maryland, 16 of which were located on the Eastern shore [
19
]. Twenty-four out of 30 sam-

Int. J. Environ. Res. Public Health 2021,18, 145 3 of 13
ples (80%) from the Eastern shore contained at least 1 detectable pesticide or degradate
compound, and 16 (53%) contained at least 5 detectable compounds, with the majority
of detected compounds being herbicides used for agriculture. One sample contained
11 different compounds. While no sample contained any pesticide or herbicide compounds
at concentrations exceeding established Federal drinking water standards, such standards
exist for only 4 out of all compounds detected (see supplemental data, Table S1 for list of
detected compounds). More recently, researchers Minovi and Schmitt assessed private
well water data from Wicomico and Worcester Counties to determine the extent of nitrate
contamination on the lower Eastern shore. The researchers concluded that Wicomico and
Worcester Counties have detected nitrates at levels exceeding the EPA’s safe drinking water
threshold in approximately one out of every 25 private drinking water wells [20].
Cancer statistics for the lower Eastern shore of Maryland are also high. According
to the U.S. Surveillance, Epidemiology, and End Results (SEER) database, Wicomico,
Worcester, and Somerset counties have some of the highest rates of lung cancer, colorectal
cancer, breast cancer, and melanoma in Maryland [
21
]. Wicomico and Somerset counties all
sites cancer incidence rates from 2007 to 2011 were >25% above national rates, and all sites
cancer incidence rates in Worcester county were 10–25% above national rates. In addition,
the mortality rates for several types of cancers, including lung and colon cancer, are higher
in Wicomico, Somerset and Worcester counties compared to national rates, suggesting
more advanced disease at time of diagnosis.
Given the high incidence of several cancer types, the potential for ground water
contamination, and the popularity of private well water use in this rural region, evaluating
the relationship between cancer diagnosis and water source on the lower Eastern shore
bears consideration. The purpose of this exploratory study was to characterize residential
water source among patients on the lower Eastern shore of Maryland with a known
diagnosis of melanoma, lung, breast, or colorectal cancer, and to determine characteristics,
such as more advanced cancer stage, that might be associated with private well water use.
We also compared residential private well water use among cancer patients in our study to
private well water use for the general regional population.
2. Materials and Methods
2.1. Study Design
This study was approved through the Western Institutional Review Board. A retro-
spective chart review was conducted on all patients diagnosed with colon, lung, melanoma
or breast cancer at a regional hospital from 1 January 2017 through 31 December 2018. This
regional hospital serves as the largest hospital on the lower Eastern shore, with a catchment
area that spans Wicomico, Worcester and Somerset Counties, as well as Sussex County in
Delaware and Accomack County in Virginia. For most individuals living in these counties,
the closest alternative hospital is located at least an hour away, and for some individuals,
almost three hours away. While some individuals may seek subsequent or follow-up care
outside of this regional hospital, the geographic isolation of the lower Eastern shore ensures
that the majority of individuals living in this region seek initial diagnostic care locally. For
example, there were 511 newly diagnosed cases of colon, lung, melanoma or breast cancer
diagnosed in Wicomico, Worcester and Somerset Counties in the year 2016 [
21
]. According
to institutional cancer registries, approximately 90% of these cases were diagnosed at this
regional hospital [22].
Colon, lung, melanoma and breast cancers were selected for investigation because
the incidence or mortality of each of these cancers is reported to be >10% higher on the
lower Eastern shore compared to national rates [
21
]. Bladder cancer, a type of cancer
that has been linked to agricultural pollution by other studies, was not included in our
study due to low case numbers. Eligible patients were
≥
18 years of age. Exclusion
criteria included insufficient chart documentation, residential address outside of Wicomico,
Worcester or Somerset counties, or atypical cancer diagnosis (angiosarcoma of the breast,
colonic neuroendocrine tumor, etc.).

Int. J. Environ. Res. Public Health 2021,18, 145 4 of 13
Age at time of cancer diagnosis, current residential address, sex, race and cancer type
were recorded. Cancer stage, as well as smoking history, family history and prior cancer
history were documented. Residential water supply was determined using the patient’s
residential address and municipal water records.
2.2. Regional Private Well Water Statistics
Regional private well water utilization was determined using 2010 U.S. Census data,
source water assessment documents for Wicomico, Worcester and Somerset Counties, as
well as the comprehensive water and sewer plan for each county [
23
–
34
]. To determine the
overall percentage of individuals on the lower Eastern shore who rely on residential private
well water, we combined the number of individuals in each county relying on private well
water and divided this by the total population for the region.
2.3. Data Analysis
Descriptive statistics were reported, including residential water supply for our total
study population and for our study population stratified by county. Rates of residential
private well water supply were compared between our study population and baseline
regional population using the chi-square or Fisher’s exact test. All tests were two-tailed
with a significance level of p< 0.05. Ability to control for confounding variables in our
current exploratory study was limited due to the study design. Factors such as age, sex,
and race were not controlled during our data analysis. We did evaluate the relationships
between residential water supply and age of cancer diagnosis, cancer type, cancer stage,
smoking history, family history and prior cancer history using Fisher ’s exact test.
3. Results
3.1. Patient Characteristics
A total of 1248 charts were reviewed. A total of 420 cases had a residential address
outside of Wicomico, Worcester and Somerset Counties (34%), and were therefore excluded
from analysis. A total of 48 cases were excluded from analysis due to insufficient data
(4%), 17 cases were excluded due to being duplicate cases (1%), and 17 cases were excluded
due to rare cancer/non-cancerous diagnosis (1%). A total of 746 cases were ultimately
eligible for analysis (60%). Baseline demographic characteristics and medical histories are
summarized in Table 1. Sixty percent of patients resided in Wicomico County and 80% of
patients self-identified as Caucasian. The median patient age was 67.2 years (SD
±
11.9).
The majority of patients were female (67%), diagnosed with breast cancer (40%), had early
stage cancer (63%), a prior or current smoking history (62%), a family history of cancer
(68%), and no prior cancer history (68%).
3.2. Cancer Patient Private Well Water Utilization
The majority of cancer patients on the lower Eastern shore of Maryland lived in homes
that relied on private well water (n= 428, 57%). At the county level, residential water
source varied (Table 2). In Wicomico County, 64% of cancer patients lived in homes that
relied on private well water (n= 285). In Worcester County, 41% of cancer patients lived in
homes that relied on private well water (n= 81), while in Somerset County, 60% of cancer
patients relied on residential private well water (n= 62).

Int. J. Environ. Res. Public Health 2021,18, 145 5 of 13
Table 1.
Demographics of Cancer Patients on the Lower Eastern Shore of Maryland; 1 January
2017–31 December 2018.
Characteristic n= 745 (%)
Well Water Use
Yes 428 (57)
No 317 (43)
County
Wicomico 444 (60)
Worcester 198 (27)
Somerset 103 (14)
Sex
Male 247 (33)
Female 498 (67)
Age (years)
≤60 209 (28)
61–70 241 (32)
71–80 197 (27)
≥81 86 (13)
Race
White 596 (80)
Black 134 (18)
Other 15 (2)
Diagnosis
Breast 297 (40)
Lung 260 (35)
Melanoma 106 (14)
Colon 82 (11)
Stage
Early 471 (63)
Advanced 273 (37)
Smoking History
Yes 462 (62)
No 283 (38)
Family History of Cancer
Yes 517 (69)
No 228 (31)
Prior History of Cancer
Yes 242 (32)
No 503 (68)
Table 2.
Residential Water Source for Cancer Patients on the Lower Eastern Shore by County; 1
January 2017–31 December 2018.
Characteristic n= 745 (%)
Water Source
Private Well Public Water
County
Wicomico 286 (64) 159 (36)
Worcester 81 (41) 117 (59)
Somerset 62 (60) 41 (40)
3.3. Regional Private Well Water Utilization
According to the 2010 U.S. Census, 98,733 individuals live in Wicomico County [
23
].
Approximately 68% of housing units in Wicomico County, or 67,138 individuals, are on
public or community water systems [
24
–
28
]. A total of 32 percent of housing units in
Wicomico County, or 31,595 individuals are on private individual well systems.
According to communications from the Worcester County Department of Environ-
mental Programs, anywhere between 67% and 80% of the 52,276 residents of Worcester

Int. J. Environ. Res. Public Health 2021,18, 145 6 of 13
County rely on public water systems [
29
–
33
]. For the purpose of this study, we estimated
that an average of 73% (38,161) of Worcester County residents rely on public water systems,
and 27% (14,115) rely on private well systems [23].
Somerset County is reported to have a population of 26,470 individuals [
23
]. The
county estimates that approximately 5223 dwellings, or 12,706 individuals, receive drinking
water from public municipal, county or community water systems (48%) [
34
,
35
]. Approx-
imately 5555 dwellings, or 13,764 individuals, rely on private, individual water systems
(52%).
With the three counties combined, we determined that 34% of individuals on the
lower Eastern shore of Maryland rely on residential private well water (59,474/177,479).
3.4. Comparison of Private Well Water Use between Populations
Our study found that on the lower Eastern shore of Maryland, cancer patients relied
on residential private well water more than individuals in the general regional population
(57% vs. 34%, p< 0.001) (Figure 2). Wicomico County cancer patients used residential
private well water more than the general Wicomico County population (64% vs. 32%,
p< 0.001
). Similarly, Worcester County cancer patients used residential private well water
more than the general Worcester County population (41% vs. 27%, p= 0.02). No significant
difference was found between residential private well water use for Somerset cancer
patients and the general Somerset County population.
Int. J. Environ. Res. Public Health 2021, 18, x 6 of 13
According to communications from the Worcester County Department of Environ-
mental Programs, anywhere between 67% and 80% of the 52,276 residents of Worcester
County rely on public water systems [29–33]. For the purpose of this study, we estimated
that an average of 73% (38,161) of Worcester County residents rely on public water sys-
tems, and 27% (14,115) rely on private well systems [23].
Somerset County is reported to have a population of 26,470 individuals [23]. The
county estimates that approximately 5223 dwellings, or 12,706 individuals, receive drink-
ing water from public municipal, county or community water systems (48%) [34,35]. Ap-
proximately 5555 dwellings, or 13,764 individuals, rely on private, individual water sys-
tems (52%).
With the three counties combined, we determined that 34% of individuals on the
lower Eastern shore of Maryland rely on residential private well water (59,474/177,479).
3.4. Comparison of Private Well Water Use between Populations
Our study found that on the lower Eastern shore of Maryland, cancer patients relied
on residential private well water more than individuals in the general regional population
(57% vs. 34%, p < 0.001) (Figure 2). Wicomico County cancer patients used residential pri-
vate well water more than the general Wicomico County population (64% vs. 32%, p <
0.001). Similarly, Worcester County cancer patients used residential private well water
more than the general Worcester County population (41% vs. 27%, p = 0.02). No significant
difference was found between residential private well water use for Somerset cancer pa-
tients and the general Somerset County population.
Figure 2. Residential private well water use for cancer patients compared to county population.
3.5. Private Well Water Use and Patient Factors
Patients diagnosed with cancer at ≤70 years of age were more likely to rely on resi-
dential private well water compared to patients diagnosed over the age of 70 (61% vs.
52%, p = 0.01). There were no differences in sex, race, or family, smoking or prior cancer
history between cancer patients using residential private well water versus public water
(Table 3).
0
10
20
30
40
50
60
70
Total Population Wicomico
County
Worcester
County
Somerset
County
Private Well Water Use (%)
Population
Cancer Patients
General County
Figure 2. Residential private well water use for cancer patients compared to county population.
3.5. Private Well Water Use and Patient Factors
Patients diagnosed with cancer at
≤
70 years of age were more likely to rely on resi-
dential private well water compared to patients diagnosed over the age of 70 (
61% vs. 52%
,
p= 0.01). There were no differences in sex, race, or family, smoking or prior cancer history
between cancer patients using residential private well water versus public water (Table 3).

Int. J. Environ. Res. Public Health 2021,18, 145 7 of 13
Table 3.
Patient Demographics for Cancer Patients on the Lower Eastern Shore by Residential Water
Source; 1 January 2017–31 December 2018.
Characteristic n= 745 (%) p-Value
Water Source
Private Well Public
Sex
Male 151 (61) 95 (39) 0.13
Female 277 (56) 222 (44)
Age (years)
≤70 276 (63) 174 (37) 0.01
>70 152 (51) 143 (49)
Race
White 346 (58) 250 (42)
0.69 **
Black 75 (56) 59 (44)
Other * *
Diagnosis
Breast 160 (54) 137 (46)
0.03 **
Lung 143 (55) 117 (45)
Melanoma 69 (65) 37 (35)
Colon 56 (68) 26 (32)
Stage
Early 271 (57) 201 (43) 1.0
Advanced 157 (58) 116 (42)
Smoking History
Yes 257 (56) 205 (44) 0.22
No 171 (60) 112 (40)
Family History of Cancer
Yes 298 (58) 219 (42) 0.87
No 130 (57) 98 (43)
Prior History of Cancer
Yes 136 (56) 106 (44) 0.64
No 292 (58) 211 (42)
* Data suppressed to preserve patient privacy. ** Differences between patients relying on private well water and
public water were analyzed using Fisher’s exact test for all analyses except “Age” and “Diagnosis,” which were
analyzed using the chi-square test.
Cancer diagnosis type differed between patients relying on private well water versus
public water, with higher frequencies of colon cancer and melanoma patients relying on
private well water compared to patients diagnosed with breast and lung cancer.
Because secondary cancers can possibly be related to treatment toxicity from a previous
cancer, a sensitivity analysis was performed to restrict analyses to only cases lacking
a history of prior cancer diagnosis. Patient factors and residential water source were
analyzed. Patients diagnosed with cancer at
≤
70 years of age were again more likely to
rely on residential private well water compared to patients diagnosed over the age of 70
(61% vs. 51%, p= 0.03). No new significant differences were noted in residential private
well water use between our original analysis and our sensitivity analysis.
4. Discussion
4.1. Cancer Patients and Residential Private Well Water Utilization
Approximately 38% of the U.S. population depends on groundwater for its drinking
water supply [
36
]. However, groundwater is susceptible to contamination. Due to the
common use of fertilizers and pesticides/herbicides, and the presence of animal waste
and by-products, agricultural non-point source pollution is a leading cause of impaired
water quality and ground water contamination in the U.S. Previous studies have confirmed
that in coastal watersheds, the amount of nitrate contamination found in groundwater is
related to the proportion of agricultural land [
36
]. Rural, agricultural regions are therefore
at higher risk for groundwater contamination and its potential health implications.

Int. J. Environ. Res. Public Health 2021,18, 145 8 of 13
The lower Eastern shore of Maryland is a rural, heavily agricultural region that has a
strong economic history of farming and large-scale chicken breeding. According to the EPA,
over 600 million chickens are produced yearly on the Eastern shore and the neighboring
county of Sussex, Delaware [
18
]. These birds, in turn, produce vast quantities of animal
by-products including nitrates/nitrites, ammonia, arsenic and phosphorus. Contamination
from these by-products has been shown to contribute to poor water quality of local surface
waters, which in turn raises concerns over groundwater pollution. In fact, prior research has
confirmed the presence of nitrates and agricultural pesticides in sampled well water from
across the Eastern shore. While a full review of the detected groundwater contaminants
on the Eastern shore is beyond the scope of this study, a brief list of contaminants previ-
ously detected by government agencies has been included in our supplemental data (see
Tables S2 and S3 [19,24–28,30–35]).
Our study found that 57% of cancer patients on the lower Eastern shore use residential
private well water, which is notably higher than the rate of private well water used
nationally (14%), the rate of private well water used in the overall state of Maryland
(19%), and the rate of private well water used by the lower Eastern shore population
in general (34%) [
1
,
36
]. Though interpretation of our findings was limited by lack of
causality, our study results were striking. Prior research has shown that proximity to farms
and animal feeding operations is associated with increased risk for private well water
contamination [
37
–
41
]. In addition, studies have shown that up to 50 percent of private
wells tested do not meet at least one federal health-based drinking water standard [
42
–
46
].
Given the known risk of private well contamination in agricultural regions, as well as the
known health implications of drinking contaminated well water, the association between
private well water use and cancer diagnosis in this region warrants further investigation.
At the county level, our study found that patients living in Wicomico County and
Worcester County relied on residential private well water more than general county statis-
tics. Interestingly, Somerset County had no significant difference in residential private
well water use between cancer patients and the general county population. This difference
may stem from inter-county variation in policies regarding groundwater safety or animal
feeding operations, and would need to be explored further in future studies.
Interestingly, our study found that cancer patients
≤
70 years of age were more likely to
rely on residential private well water compared to patients over the age of 70. These results
should be interpreted with caution, as we did not control for potentially confounding
variables. However, it is well established that advancing age is a risk factor for cancer
development, while environmental exposure to carcinogenic materials can increase risk of
cancer development at younger ages [
47
–
49
]. The association between well water exposure
and younger age of cancer diagnosis in this region hints at a potentially carcinogenic
relationship between these two variables, and again supports the need for additional
studies examining the causality of private well water exposure and cancer risk in this
region.
Finally, we found that cancer patients relied on residential private well water differ-
ently depending on their cancer diagnosis. All patients, regardless of cancer type, relied
on residential private well water more than public water. However, colon cancer and
melanoma patients used residential well water at higher frequencies compared to breast
and lung cancer patients. Our ability to interpret these findings is limited though, given
that we did not control for potentially confounding variables. Factors such as county of
residence or age may account for these findings.
4.2. Limitations
Our study possessed several limitations. Due to the study design, we could not
establish causality between residential private well water use and cancer diagnosis on
the lower Eastern shore of Maryland. Importantly, our study did not sample and test the
residential water supply of any of the patients included in this study. Without performing
water testing, we cannot truly establish a connection between residential water source and

Int. J. Environ. Res. Public Health 2021,18, 145 9 of 13
cancer diagnosis. In addition, ability to control for confounding variables in our current
exploratory study was limited due to the study design. Our study compared private well
water use in cancer patients to general county statistics. While we were able to determine
the percentage of each county that relied on residential private well water, we were unable
to determine the age and race of this particular population at the county level, making
controlling for these variables difficult. In addition, at the time of the study design, there
was little historic data describing variables that might influence private well water use in
this region. To preserve data accuracy, we did not wish to control for variables that may
not be truly affecting our outcomes.
Diet was another factor that we were unable to evaluate and control for in our current
study. It is well known that diet can influence cancer risk, and consuming carcinogenic
foods, such as foods high in nitrates, can potentially increase cancer risk [
50
,
51
]. As this
was a retrospective study, our ability to assess various patient factors was dependent on the
data collected at the time of service. Extensive dietary review is not typically performed
on patients diagnosed with cancer at this regional hospital. Similarly, extensive dietary
information is not typically recorded at the county level. We were therefore unable to
assess the extent dietary intake of potentially carcinogenic foods may be confounding our
findings.
Because of the retrospective nature of this study, we were unable to confirm length of
residency, or whether patients relied on residential tap water for their drinking water. In
addition, while patient’s home address was determined via chart review, we were unable
to confirm that the currently listed home address was also the patient’s home address
at time of initial cancer diagnosis. Despite these limitations, however, this exploratory
study brings to light an important public health issue, and provides grounds for further
investigation.
4.3. Public Health Implications
To our knowledge, the current study is the first to evaluate private well water use on
the lower Eastern shore of Maryland and its relationship with cancer diagnosis. At this
time, the results of our study should not change local public or environmental policies,
nor should they cause undue distress among local citizens who may consume private
well water. While the results of our study are striking, they are not causal. As mentioned
previously, we do not have data at this time confirming that private well water consumption
in this region causes cancer.
That being said, the results of our study certainly signal a need for additional research
on this topic. While our findings may simply be the result of confounding factors, alterna-
tively they may truly reflect an increase in cancer risk for individuals on the lower Eastern
shore who rely on residential private well water. A study published in 2018 by Schullehner
et al. found an increased risk for colon cancer in persons exposed to higher levels of
drinking water nitrate compared to persons exposed to lower levels [
52
]. Similarly, another
study found that long term ingestion of elevated nitrate in drinking water was associated
with increased risk of bladder cancer among postmenopausal women [
53
]. A meta-analysis
performed by Saint-Jacques et al. in 2014 showed that arsenic in drinking water is associ-
ated with increased risk of bladder and kidney cancers [
54
]. These studies highlight the fact
that drinking water research has the potential to impact the health of a large population,
and its findings could have far reaching policy and monitoring implications.
4.4. Future Directions
The results of our study suggest that a relationship may exist between private well
water use and cancer diagnosis on the lower Eastern shore of Maryland. Though there
are many limitations to our study, our study certainly suggests that additional research is
needed to clarify the relationship between these two variables. Additional steps to confirm
this relationship would include a case-control study to compare well water use among
cancer patients and individuals without a prior history of cancer. In this future study,

Int. J. Environ. Res. Public Health 2021,18, 145 10 of 13
determining if participants primarily drank tap water vs. bottled water, or used a drinking
water filtration device, would be beneficial. In addition, determining how many glasses
of tap water participants consumed per day, and the duration of home residency, would
be interesting and provide further insight into this complicated yet highly relevant public
health issue.
Alternatively, geographical variation in cancer incidence could be examined across the
lower Eastern shore of Maryland. Spatial cluster analysis could be performed to determine
whether spatial clusters in cancer incidence are associated with the presence of concentrated
animal feeding operations or agricultural land use. This form of analysis can be difficult
for diseases with complex etiology and long latency such as most cancers. Nonetheless,
cancer cluster investigations in the past occasionally have led to the discovery of important
pathways in the etiology of specific cancers, such as vaginal cell carcinoma and scrotal
cancer [55,56].
Finally, additional research could include testing of private well water quality across
the lower Eastern shore of Maryland for microbiological and chemical contaminants. One
similar study, performed by Murray et al., examined private well water quality across
four counties in Maryland. The study found that nearly half of tested wells did not meet
federal health-based drinking water standards [
42
]. Interestingly, the study did not find a
relationship between animal feeding operations and well water contamination; however,
this study did not include well water samples from Wicomico, Worcester or Somerset
counties.
5. Conclusions
In conclusion, the majority of cancer patients on the lower Eastern shore of Maryland
relied on residential private well water, and cancer patients used residential private well
water more than the general regional population. Younger cancer patients in this region
were also more likely to rely on residential private well water compared to older cancer
patients, though interpretation of these results should be made with caution due to inability
to control for confounding variables. The findings of our study highlight the need for
further research evaluating the relationship between well water exposure and cancer risk
in this vulnerable region.
Supplementary Materials:
The following are available online at https://www.mdpi.com/1660- 460
1/18/1/145/s1, Table S1: Pesticides and degradate compounds identified on the Eastern shore by the
U.S. Geological Survey, 2001–2004. Adapted from data published by the U.S. Geological Survey [
19
],
Table S2: Inorganic compounds, radionuclides, volitile organic compounds and synthetic organic
compounds that were detected at least once either above 50% or 100% of their MCL in Wicomico
County public water system (1991–2003) [
24
–
28
], Table S3: Inorganic compounds, radionuclides,
volitile organic compounds and synthetic organic compounds that were detected at least once either
above 50% or 100% of their MCL in Worcester 3County public water system (1991–2005) [
30
–
32
],
Table S4: Inorganic compounds, radionuclides and volitile organic compounds that were detected
at least once either above 50% or 100% of their MCL in Somerset County public water system
(1994–2002) [34,35].
Author Contributions:
A.D. conceived of this study, acquired study funding, contributed to the
study design, and performed data collection. S.K. performed data collection. V.H. performed data
analysis. All authors were involved with drafting and revising this manuscript for content. All
authors have read and agreed to the published version of the manuscript.
Funding:
This project was supported by a Richard A. Henson Research Institute Investigator Endow-
ment.
Institutional Review Board Statement:
We believe the study is exempt under 45 CFR § 46.104(d)(4)
because identifiable health information will be accessed from medical records and recorded in such a
manner that the identity of the human subjects cannot be readily be ascertained directly or through
identifiers linked to the subjects, and the investigator will not contact the subjects of re-identify
subjects. Ethical review and approval were waived for this study due to retrospective nature of this
study.

Int. J. Environ. Res. Public Health 2021,18, 145 11 of 13
Informed Consent Statement:
Patient consent was waived due to the retrospective nature of this
study.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author. The data are not publicly available in an effort to strictly ensure patient
privacy.
Acknowledgments:
We thank the Richard A. Henson Cancer Institute for its support and encourage-
ment of this project.
Conflicts of Interest: The authors have no potential or actual conflict of interest.
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