MPs were also identified. For studies to be considered, they
had to investigate items commonly consumed by humans and
report MP concentration as exact values (total count in a single
sample) or as a mean. One of the studies considering airborne
plastics
11
did not provide a mean so the median values were
extracted with the caveat that these are likely lower than means
given the distribution of the data. In this instance, the study
measured all particulates in the air of two apartments, an office,
and outside of an office building and determined that only 33%
of these particles were synthetic, petroleum-based polymers, so
the median number reported was adjusted to 33% of the total.
To ensure consistency, median values were also extracted from
the second study addressing airborne plastics. For all studies,
the type of MPs (e.g., fiber, bead) found was also noted, as well
as the type of chemical method (if any) used to verify whether
particles were plastic. Twenty-six studies were identified by this
process, specifically investigating the following consumption
groups: fish, shellfish, added sugars, salts, alcohol, water, and
air (Table S1). Only studies assessing items that are commonly
consumed by people were considered (e.g., whole fish, fish
tissue, table salts, tap water, refined and raw sugars, etc.). All
data were obtained from tables and text where possible; if
necessary, the software GraphClick was used to retrieve data
from figures.
12
A total of 402 data points, which represents
over 3600 processed samples, were collected from the 26
studies where each data point represents the concentration of
microplastics within a specific item presented within a study,
commonly composed of multiple replicates (Table S1).
Recommended dietary intakes for Americans were deter-
mined using the Dietary Guidelines for Americans 2015−2020,
eighth edition report, by the U.S. Department of Health and
Human Services.
13
Average consumption was separated by sex
and age: male adults, female adults, male children, and female
children. Adults were considered to be 19 years of age or older.
When consumption values were presented as ranges across an
age group, as was the case with seafood, the mean of the range
was used. During this process, we estimated caloric intake
assuming a moderately active lifestyle (as this seemed to be the
most widely applicable choice), which recommended calorie
intakes of 1965, 2733, 1694, and 2133 for male children and
adults, and female children and adults, respectively. Although it
was noted that the difference between sedentary/moderate and
moderate/active could be up to 400 calories per day depending
on age, this decision only directly affected the recommended
added sugar intake, which is 10% of consumed calories. To
account for the amount of honey consumed by the American
population, the per capita consump tion of honey was
subtracted from sugar consumption. The Department of
Agriculture’s National Agricultural Statistics Service Annual
Honey Report estimates Americans consume 1.61 pounds of
honey per year or 2.00 g per day. The amount of sugar
remaining was then assumed to be made up of the other forms
of sugar considered (e.g., refined).
To determine microplastics consumed via drinking water,
separate calculations were made for 100% tap water, 100%
bottled water, and a composite estimate of average current tap
and bottled water consumption. For the composite estimate,
the average per capita daily consumption of 0.436 L of bottled
water was used, with the remaining recommended water
consumption being made up by tap water; this was determined
to be roughly 17% bottled water and 83% tap water, based on
the amount of bottled water consumed per capita in the U.S.
relative to the recommended water consumption.
14
Thus, in
this instance, water was considered a combination of bottled
and tapped sources based on the average per capita water
consumption and The National Academy’s recommended
consumption of water for the age group and sex considered.
15
As the only available data on microplastics in alcohol were
concentrations within beer, the reported amount of per capita
alcohol consumption by adult men and women was evaluated
in terms of beer.
16−18
As the World Health Organization
(2014) reports male and female per capita consumption of
13.6 and 4.9 L of alcohol, it was assumed this consumption was
comprised entirely of beer. As the report lists beer as the most
commonly consumed alcohol for both sexes, by a large margin,
this is a reasonable assumption.
17
Mean respiration rates for different age groups and sexes
were obtained from the U.S. Environmental Protection Agency
exposure factors handbook 2011, with values ranging from
3.4−19.3 m
3
/day.
19
The age groups in this report were
combined and a veraged into the previously mentioned
categories of male children and adults, and female children
and adults; however, in this instance, adults were considered to
be 22 years of age or older due to the preformed groupings.
Data Analysis. The literature review resulted in MP
concentrations within commonly consumed items that could
be separated into the following categories: air, alcohol, bottled
water, honey, seafood, salt,sugar,andtapwater.MP
concentrations were converted, where necessary, to particles
per gram, liter, or cubic meters, depending on whether the
study focused on foods, liquids or air, respectively. At the study
level, a mean concentration was determined from all the items
within a single category (e.g., all the fish and bivalve values in
the seafood category). As a result, in studies that evaluated the
MP concentration within multiple items (e.g., bottled and tap
water), each case was treated independently and the average
for each item was determined. As the MP concentration across
items was never pooled during the analysis, treating these cases
as independent did not compromise our results.
The average intake of MPs associated with the daily
consumption of each item was determined. The mean MP
concentration for each study was determined within the
various items (Table S1). Subsequently, the mean and
associated standard deviation for each of the items was derived
from the study means. Tap water and sugar were comprised of
single studies. In these instances, the mean and standard
deviation were determined within each study (as compared to
across studies) using the five and 14 MP concentration values
presented within the sugar and tap water studies, respectively.
The number of MPs consumed for each age group and sex was
then determined by multiplying each of the microplastic
concentrations by the respective daily consumption value of
each item (Table S1, S2, and S3).
The annual consumption of MP was determined. The mean
MP concentration for each study was determined within the
various items as outlined above (Table S1). In a similar fashion
to the previously discussed mean and associated standard
deviation calculations, the mean and variance for each of the
items were derived from the study means. Again, tap water and
sugar were comprised of single studies. The mean and variance
for these items were determined within each study (as
compared to across studies). The number of microplastics
consumed annually by each age group and sex was determined
by multiplying each of the microplastic concentrations by the
respective annual consumption value of each item. To
determine the average standard deviation for the annual
Environmental Science & Technology Article
DOI: 10.1021/acs.est.9b01517
Environ. Sci. Technol. 2019, 53, 7068−7074
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