1. Urban agriculture and emerging lead exposure pathways: Sustainable, but safe?
Introduction
Ciaran L. Gallagher, ’17 Environmental Chemistry, Hana Bracale, ’18 Undeclared, Shivani Kuckreja, ’16 Environmental Studies and Economics
Advisor: Daniel Brabander
Urban soils, including those in the Greater Boston Area, are an
extensive repository of lead from the historical use of leaded gasoline
and leaded paint (Clark et al., 2006, 2008). Recent research has linked
higher lead blood levels to increased exposure to soil, challenging the
paradigm of lead exposure pathways dust (Zahran et al., 2013). Instead
of considering leaded paint as the largest driver of lead exposure, dust
and urban soils with high lead concentrations are now recognized as
responsible for seasonal elevated lead blood levels.
Urban agriculture can increase food sovereignty in neighborhoods
where access to produce is limited, however it also raises new
questions about the lead exposure from fruits and vegetables grown in
this setting (Figure 1). While the exposure to lead from urban produce
gardens has been studied, the exposure to lead from urban harvested
fruit is not known. The League of Urban Canners (LUrC) is a Boston
based group which harvests food grown in residential and public spaces
for private consumption and has provided the samples for our research
from its 2014 harvest.
Results and Discussion
Figure 9: Pellet mass v. [Pb]. The
strong correlation between the pellet
mass and lead concentrations (R2 =
0.795) shows that we need to
reevaluate the analytical methods for
this matrix. This means that all [Pb]
presented here are a maximum.
Figure 6: [Pb] across Fruit. Lead concentrations (ppm) for each
sample pellet analyzed with the XRF-XEPOS. The pellets were
run in quadrature and the error bars indicate the standard
deviation between the four analyses. The samples where
[Pb]< LOD are also included. The samples numbers correlate to
the sampling location, see Figure 2B.
To make fruit pellets, we first ground the
dried fruit with the mixer mill. After five
minutes we added about 0.45g of
Spectroblend binding agent to the canister
and milled the sample for another minute.
The mass of the dried fruit and the
Spectroblend were recorded. Finally, this
homogeneous powder was placed into a
tin and pressed into a pellet using the
hydraulic press. The fruit pellets were
analyzed using the XRF-XEPOS benchtop
analytical instrument. We ran the analysis
in a vacuum and each pellet was analyzed
4x. In excel, the four analyses were
averaged and the standard deviation was
used for the error.
Conclusions
Future Works
• Visit the sampling locations in order to identify potential source pathways of
lead and characterize the growing location, in particular the ground covering.
• Compare in situ analysis of soils against the lead levels found in the fruit.
• Compare micronutrients and nutritional value of urban fruit to commercial
fruit, as we have demonstrated the ability to measure iron, potassium, and
calcium in the fruit pellets (Figure 4).
• Refine exposure model based on gender, ethnicity, socioeconomic status,
and location in the city.
• Examine the geospatial correlation between lead levels in soils and fruit
Future Works: Method Development
• A large part of this semester’s lab research has been developing the method
procedure for this matrix as this is the first time this lab has analyzed fruit
samples. This project has tested the detection limit of the XEPOS (Figure 9).
• With our current pellet making method, the sample is being diluted with
spectroblend and potentially limiting the detection of lead in the pellets. We
would like to compare the XRF analysis of a pellet with spectroblend, a pellet
without spectroblend, and a dried fruit disk for the same sample in order the
assess the most appropriate sample handling procedure.
• We could also spike the samples with a specific known amount and
determine the limit of detection for the XEPOS to develop an empirical
calibration model specific for the matrix of peaches and apples.
Acknowledgements
We would like to thank the League of Urban Canners for their instigation of this project, extensive support in acquiring samples, and continued
feedback and involvement. In particular we would like to thank Amy Jarvis, Marcus Ramsden, A Tutter, Marshall, Jamie Katz-Christy, and Sam
Musher. We also want to thank the DJB lab for their helpful critique and Professor Brabander for his guidance and mentorship.
Works Cited
• Clark, H.F., Brabander, D.J., Erdil, R.M., 2006. Sources, sinks, and exposure pathways of lead in urban garden soil. Environ. Qual. 35(6): 2066–
2074.
• Clark, H.F., Hausladen, D.M, Brabander, D.J., 2008. Urban gardens: Lead exposure, recontamination mechanisms, and implications for
remediation design. Environ. Research. 107: 312- 319.
• Lead in Drinking Water. 2015. US Environmental Protection Agency: EPA; [http://water.epa.gov/drink/info/lead/index.cfm; Apr. 10, 2015].
• Zahran, Sammy, Laidlaw, M.A., McElmurry, S.P., Filippelli, G.M., Taylor, M., 2013. Linking Source and Effect: Resuspended Soil Lead, Air Lead,
and Children’s Blood Lead Levels in Detroit, Michigan. Environ. Sci. Technol. 27:2839- 2845.
• 2013 Annual Drinking Water Quality Report. 2014. Cambridge Water Department: City of Cambridge, MA.
Figure 5: [Pb] Peach v. Apple Averages. Average lead
concentrations (ppm) of all apple and peach samples analyzed
with the XRF-XEPOS (n=23). The error bars indicate the
standard deviation between the analyses. The peach average
has a significantly higher concentration of lead than the apple
average.
Figure 4: XRF Spectrum Overlay. The raw
data from the XEPOS analysis for Apple
Sample 27 washed peeled (blue line) and
Driving Questions
Figure 7: [Pb] across Varying Sample Preparation. Average
lead concentrations (ppm) across the varying sample
preparation (unwashed, washed not peeled, washed peeled)
for the peach samples analyzed (n=14). The error bars
indicate the standard deviation between the individual
analyses. We found no significant difference of lead
concentrations between sample preparations.
1. Is the consumption of urban harvested fruit a source
of lead exposure?
2. Where is the lead in this setting coming from? Is it on
the surface of the fruit? How does simple kitchen
preparation (washing and peeling) impact the
measureable lead concentration?
3. Does lead exposure vary across fruit species?
4. How does local and community scale land use
patterns effect measured lead concentrations?
5. How do our estimates for exposure compare to the
EPA benchmark (action level) for drinking water?
Compare with City of Cambridge average drinking
water chemistry.
• As illustrated by Figure 4, the peak heights for lead in these samples is
just observable. Several samples were at concentrations less than the
detection limit.
• Initial results suggest that fruit in city centers tend to have higher
concentrations of lead (Figure 2B).
• There was no significant difference in [Pb] across sample preparations
(Figure 7). This surprised us as we expected washing to decrease the
[Pb] by washing off the lead contaminated dust.
• Lead exposure associated with the consumption of urban fruit represents
no significant health risk (Figure 8).
Methods
LUrCanner participants collected produce samples from
various parts of the Greater Boston Area over the course
of the 2014 summer and fall (n= 166, Figure 2A). These
were frozen and catalogued by species type, location and
collection date. For our initial analysis, we chose to focus
on the two most common fruit type, peaches (n=6 whole
peaches, n=14 analysis) and apples (n=3 whole apples,
n=9 analysis), and chose samples from varying trafficked
areas (Figure 2B.)
For the parameters for this project, we decided to analyze
the impact of washing and peeling fruit on lead
concentrations. These specific parameters were chosen
in an attempt to uncover where lead resides in the fruit: in
the dust on the fruit’s surface, in the peel, or in the fruit
itself.
Each fruit analyzed was cut into three samples; one was
unwashed and unpeeled, one was washed and unpeeled,
and one was washed and peeled (Figure 3). The samples
were washed with tap water in order to mimic kitchen-
washing methods. Between each sample preparation, the
cutting board and knife were washed with soap, rinsed
with regular tap water and distilled water and wiped dry.
We massed each sample and placed all samples into the
oven at 45°C for several days, until the samples’ masses
remained constant.
Figure 1: Potential Exposure Pathways of Pb in urban fruit. The
variables in our research include fruit species and sample
preparation as identified. The lead exposure from produce gardens
has been studied while the lead exposure from harvesting fruit in
contaminated soils is not yet known.
Figure 8: Exposure Estimate. Lead exposure estimate from the
consumption of 1 apple or peach per day compared to the lead
exposure estimate from drinking 32oz of Cambridge Tap water and the
lead EPA benchmark for drinking water.
Figure 3: Visual
representation of the
sample preparation methods.
Figure 2A: Greater Boston Area Map with all locations of sample collection indicated.
Figure 2B: Map of analyzed samples, peaches indicated by orange and apples indicated by
green.
Peach Sample 67
washed peeled (red line). Peaks identified for lead (Pb),
potassium (K), iron (Fe), calcium (Ca), nickel (Ni) and rubidium (Rb).