1. Lead contaminated soils: Are urban gardeners being exposed
Lead contaminated soils: Are urban gardeners being exposed? A pilot study
Michael Schmeltz MS, DrPH(c) – CUNY School of Public Health at Hunter College
Study Objective
Methods
Results
Results cont.
Local gardeners were recruited from a gardening expo at the Brooklyn Botanical Gardens in New York City. Participants agreed to a home visit to obtain soil samples and answer a questionnaire. Compensation was a free test of lead concentration in the gardening soil of participants.
To measure lead concentrations in urban soils; to explore habits and behaviors of urban gardeners; and to investigate the potential exposure pathway between urban gardeners and elevated levels of lead in urban soil.
Half of the respondents reported some renovation or construction activity which produced dust in the vicinity of the gardens. Observational notes of the gardens included front yard gardens being within 3 meters of active roadways; peeling paint from home or fencing adjacent to gardens; past history of concrete covering garden area and in areas that previously accumulated garbage.
Lead Concentrations in Soil:
The average concentration for lead in soil among all 18 soil samples taken was 373ppm. This is just below the US EPA reportable limit of 400ppm. The lowest concentration was measured at 109ppm and the highest concentration was measured at 1317ppm. In total there were four gardens that measured lead concentrations above 400ppm.
Soil Sampling and Testing:
Soil was collected from 18 gardens at 13 different homes. Each garden tested was used for both growing produce and recreational gardening. Two samples of soil were taken from each garden approximately 2 to 4 inches below the surface. A small trowel was used to remove approximately 100 g of soil. The soil samples were collected in plastic bags and later desiccated. The two samples from each garden were mixed together to get an overall assessment of the level of Pb in the garden.
Soil lead concentration was analyzed by a field portable X-ray fluorescence (FP-XRF) Olympus (Innov-X Alpha) instrument. Desiccated samples were brought to the lab where the FP-XRF was docked. Using an X-ray tube, W anode, kV, 10–50 μA, source the soil was analyzed for lead content with the FP-XRF. Two readings were taken for each sample and the results were averaged.
Background and Significance
Conclusion
Urban gardening has become increasingly popular in the past few years. While there are health benefits to gardening and growing fruits and vegetables for consumption, urban soils pose a risk to health due to contamination from heavy metals. Lead in particular is one toxic metal that is ubiquitous in the urban environment.
Urban gardens provide a pathway for soil dust to invade the home by tracking soil in from shoes, pets, and via resuspension and deposition from wind and other normal weather patterns. With the popularity of urban gardens on the rise the possibility of exposure is also increased with increased number of hours spent in the garden as well as consuming produce grown in contaminated soil.
Lead Concentration (ppm)
US EPA reportable limit
Previous use of the gardening site, atmospheric deposition, fires, and runoff from metal surfaces are some of the other possible sources of lead. It has also been shown that older homes built before 1920 have the highest mean values of lead in gardens adjacent to the building followed by houses built between 1920 and Finally houses built after 1980 have the lowest mean concentrations. In addition, urban areas have a significant portion of surfaces covered by asphalt and concrete allowing for runoff and road grit to accumulate in green spaces.
Selected lead concentrations in gardening soil
Results from this pilot study suggest that most of the gardeners do not wear personal protective equipment and ‘washing-up’ may not be as thorough as needed. This also indicates that many urban gardeners may be unaware of the threat of lead contaminated soil. Education about soil contamination and proper procedures for cleaning and remediation of contaminated soil would benefit gardeners and their families to reduce the amount of soil dust that enters their home.
Questionnaire: Gardener Characteristics and Risk Behaviors
More than half the gardeners spent at least 5 or more days a week in the garden, though less than 3 hours a day gardening. The majority (70%) gardened in the spring, summer and fall. Gardening activities included yard work – raking/sweeping; digging and planting; weeding; watering; and recreational activities.
Person protective equipment (PPE) used for gardening
Although there is not a set standard for lead concentration in garden soils many studies have weighed in on the debate on what concentrations are considered “safe” to grow produce and which are considered to be “not safe”. Table 1 below gives a few examples of which concentrations researchers feel lead concentrations in soil need to be to grow produce.
Questionnaire:
Participants were asked to answer a number of questions about their gardening habits. Questions included the seasons and amount of time they gardened per week; use of PPE as well as personal hygiene after working in the garden; recreational activities in and around the garden (including eating and drinking); whether gardeners grew and consumed fruits, vegetables or herbs; condition of area before it became a garden; if any soil was added to the area; and whether or not children played in the garden.
Observations of construction/renovation activity near or around the gardening area and the proximity of the gardens to roadways was noted.
Table 1. Soil lead level limits for growing food in gardens.
Limits
Source
>100 ppm lead do not grow produce with children, <300 ppm lead produce can be grown without children
Rosen, 2002(25)
≥400 ppm lead, do not grow produce
Finster et al (15)
Between 400 and 1000 ppm do not grow leafy greens or root crops. Above 1000 ppm do not grow any produce.
Stehouwer & Macneal, 1999(26)
Between 400 and 1200 ppm do not grow leafy greens or root crops. Above 1200 ppm do not grow any produce.
Angima & Sullivan, 2008(27)
Between 500 and 1000 ppm do not grow leafy greens or root crops. Above 1000 ppm do not garden in soil.
Logan, 1993(28)
About half of respondents ate or drank while working in the garden. All of respondents grew some sort of produce that was consumed (vegetables, herbs or fruit) in their gardens. Almost all, 91%, reported washing produce by just rinsing with water.
New soil was added to 73% of respondents’ gardens during at the start of a new growing season with an average of 3.18 inches of soil being added to these gardens. Soil was either bought at a store (36%), brought in from another location (10%) or a combination of the two (27%).
Potential garden site
Potential garden site
Cross-section of setting demonstrating typical urban soil Pb patterns
(modified from Olszowy et al and Laidlaw and Taylor, 2010)
Urban gardening includes recreational gardening and growing herbs, vegetables and fruits for consumption, the latter which has become increasingly popular. Part of the ingestion exposure pathway is related to plants that are grown in lead contaminated soil. Plants can absorb lead from the soil though it is dependent on the species of plant, the chemical composition of the soil and the amount of lead in the soil. Soil ingestion is not the main cause of lead poisoning and there are a variety of sources from which we are all exposed to lead. Urban gardening and consumption of urban grown produce may contribute to the already elevated body burdens of lead from other sources.
Source: Modified from Witzling et al
Urban gardening should be a fun and healthy activity for people. More steps should be taken to encourage urban gardening and with it education on how to do it properly and safely especially if there is a threat of contaminated soil.
Personal hygiene after gardening
Acknowledgements
Thank you to both Dr. Jean Grassman and Dr. Joshua Cheng at Brooklyn College for their guidance in this project and a special thank you to all the volunteer gardeners who participated.
Typical backyard garden in New York City