Hunting Down Hidden Dangers and Health Benefits of Urban Fruit

03 Nov 2015 --- Forgotten trees from long lost orchards and 20th-century city landscaping are being rediscovered in urban areas, and their fruits are proving not only largely free of urban pollutants, but more nutritious than their retail counterparts.

Scientists at Wellesley College have joined forces with the League of Urban Canners (LUrC), based in Cambridge/Somerville and greater Boston area, to collect and eventually analyze 166 samples of apples, peaches, cherries and other urban fruits and herbs, collected from remnants of historical farms, urban parkland, and residential properties. The efforts grew out of concern for a LUrC member who was found to have high levels of lead in their blood. Members of LUrC wanted to make sure that the urban fruits they were harvesting and processing were not harboring toxic metals.

"This is a story with a good ending: not much lead in these urban harvested fruit," said Wellesley geosciences and environmental studies professor Dan Brabander, who has previously studied lead exposure risk in urban gardens and in areas impacted by historical mining activities.

The LUrC study investigated the concentrations of lead in urban fruits when they were peeled and unpeeled as well as washed and unwashed. That was intended to distinguish whether the fruits were taking up lead internally or being contaminated by dry deposition from the air or from soil dust.

"We found there was no difference between these variables," said Ciaran Gallagher, an undergraduate researcher majoring in Environmental Chemistry at Wellesley College, who will be presenting the research on Monday, Nov. 2 at the annual meeting of the Geological Society of America in Baltimore. Gallagher will be co-presenting with geoscience undergraduates Hannah Oettgen and Disha Okhai.

The researchers also looked at arsenic in the fruits, because in older orchards farmers commonly used lead arsenate as a pesticide. "So we are keeping an eye on places where this pesticide might have been historically applied." To date the researchers have not found evidence of use in the LUrC samples.

For the lead analysis, fourteen urban and eight commercial fruit samples were dried in a fruit dehydrator to mimic methods used by LUrC members in their home kitchens, and analyzed for trace elements. Gallagher and her colleagues found that the lead concentrations in urban apples ranged from 0.5 to 1.2 ug/g (dry weight basis). They then looked at the estimated consumption of the fruit to model how much lead the urban fruit eaters were being exposed to. The resulting finding suggest that eating urban fruit is not a significant source of lead exposure, when compared to the EPA regulated benchmark for lead in drinking water.

In addition to lead and arsenic, they also looked into the nutritional value of urban fruit. They compared micronutrient levels with those in commercially grown fruits and found that calcium concentrations in urban apples and peaches are more than 2.5 times those in their commercial counterparts. Concentrations of calcium and iron were higher in urban fruits for every fruit type tested, and manganese, zinc, magnesium, and potassium concentrations were higher in certain urban fruit types. On average, urban fruit contains a wider range of micronutrients than its commercial counterparts.

"When they grow in a commercial setting the soils can become quite impoverished," Brabander explained. "In the urban setting where the trees sampled tend to be older perhaps they are able to shuttle micronutrients from a wider and more diverse range of horizons." Planned future soil coring work into urban soils will try to figure out the mechanism of nutrient transfer in this unique setting.

"That's not to say that all urban produce is safe to eat, however, because local conditions vary and antique fruit trees are found in some very unexpected -- and sometimes very polluted places, like along major roadways," said Brabander.

"By working with the Wellesley researchers the LUrC members are able to get a much broader, clearer look at the health benefits and any potential health threats from urban fruit than they ever could have if they had randomly spot checked fruits," said Brabander.

"The citizen-science component to both study initiation and sampling is so central to how this project has been conceived and executed to date," said Gallagher. "Simply stated, without the League of Urban Canners, this project would not have been possible."

Brabander concludes, "The intersection of urban geohealth and citizen science is an emerging research paradigm for prioritizing projects that have immediate implications for designing best practices that promote a wide expression of safe and sustainable urban agriculture."