A striking new study has found eggs from hens kept as pets in urban backyards can contain up to 40 times more lead than eggs from commercially farmed hens. The researchers recommend those living in inner-city locations test their soil for contaminants before raising chickens or growing food.
Millions of households in the United States keep chickens, and those numbers have reportedly increased since the pandemic kicked off in 2020. The growing popularity of the trend has been spurred on by local food movements, inspiring people to produce their own food.
“Surveys show that backyard chicken owners are concerned about where their food comes from, how it was produced and possible risks associated with eating industrially produced meat and eggs,” explained a team of researchers from the University of California in 2018. “They believe their birds have a better quality of life and produce safer and more nutritious eggs and meat than commercially raised versions.”
Focusing on the trend of backyard chickens as a local source of eggs, those University of California researchers suggested a distinct lack of regulatory oversight meant the practice was rife with dangers to human health and animal welfare. Now, a team of Australian researchers has flagged another concern with eggs from backyard hens: lead contamination.
Following earlier findings indicating eggs from backyard hens in inner-city locations can contain higher-than-average lead levels, the new study set out to investigate the exact sources of lead exposure and what specific environmental lead levels can be considered safe for raising chickens. To do this, the researchers assessed chickens in 55 residential homes across urban Sydney.
Lead levels were tracked in the chickens, and their eggs. Contaminants were also measured in drinking water, chicken feed and soil, for every location.
While the researchers note there are no global standards for safe levels of trace metals in eggs, the findings revealed eggs from backyard hens contained up to 40 times more lead than what can normally be found in commercial products.
“The average level of lead in eggs from the backyard chickens in our study was 301µg/kg,” the researchers recently reported in The Conversation. “By comparison, it was 7.2µg/kg in the nine commercial free-range eggs we analyzed.”
A previous study looking at egg lead levels from chickens in New York City community gardens indicated 100µg/kg is probably a good threshold for safe human consumption. More than half of the eggs analyzed in the new study exceeded this threshold.
The new research also found contaminated soil was the main source of lead exposure for the backyard chickens. Lead concentrations in chicken blood and eggs could be directly linked with lead level in surrounding soil.
So, to keep eggs below the safe 100µg/kg threshold, the researchers estimate lead in soil needs to be under 117mg/kg. This is around four times lower than the current US Environmental Protection Agency (EPA) guidelines for safe lead levels in residential homes. However, the EPA does recommend significantly lower soil lead levels for gardening or food-related cultivation.
“Deeper analysis of the data showed older homes were much more likely to have high lead levels across soils, chickens and their eggs,” the researchers added. “This finding matches other studies that found older homes are most at risk of legacy contamination from the former use of lead-based paints, leaded petrol and lead pipes.”
The increasing popularity of urban agriculture has resulted in a growing body of research investigating soil contamination and its effect on food safety. This research has often focused on fruits and vegetables, finding the uptake of toxins by food can vary significantly depending on the individual crop.
The researchers behind this new study are keen to stress these findings should not stop people from engaging with urban gardening. They suggest it is a very important activity that should be encouraged, but those dwelling in urban, inner-city locations need to be aware of contamination and possibly even test their soil.
“Contaminants have built up in soils over the many years of our cities’ history,” the researchers behind the new study conclude. “These legacy contaminants can enter our food chain via vegetables, honey bees and chickens. Particularly in older, inner-city locations, it would be prudent to get their soils tested.”