Sometimes we discover things that we don’t yet understand. We like to share those findings with you, even before we make sense of them. Here is one.
This map shows the concentrations of lead in the soil at about 60 sampling sites across Manhattan, including the medians of Broadway and Central Park. Our team, led by Amy Savage and Elsa Youngsteadt, took soil cores and worked with microbial ecologist Krista McGuire at Barnard College to analyze the soils’ nutrients and contaminants. Here we’re highlighting the lead results.
At first glance, it looks like lead concentrations may be higher in the city’s forests. Why is there so much lead in some soils and not others? We don’t know yet. Perhaps there is a simple answer. Perhaps not. Perhaps, even, you can help.
For reference, according to the US CDC, uncontaminated soils contain concentrations of lead less than 50 ppm; levels below 100 ppm concentration are considered safe for gardening without any special precautions.
Many thanks to Lauren Nichols for her mad mapping skills. New York City Parks data layer courtesy NYC Open Data.
I asked several friends about this (all of whom are more familiar with NYC than I am). They had a couple of hypotheses.
My favorite (and one that could be checked by historical records) involves gas stations. I’ll quote my friend Brian Campbell (it’s his hypothesis): ” Gas stations? They’ve been closing and being redeveloped for years as Manhattan real estate has become more valuable. A lot of hte last to go were on odd shaped sites (where 72nd and broadway meet would be a weird shape that would be hard to develop and corresponds with the biggest concentration on the map, but I don’t know if there was ever a gas station there). Also, most of the gas stations still there while I lived there were in industrial zones along the west side, which would correspond with a lot of the other big samples. I know in north Brooklyn and Queens there were a lot of sites where oil storage facilities ruptured and leaked for years. Maybe something similar happened at gas stations before gasoline went unleaded?”
The second hypothesis (via Mick Kulikowski) is that the lead levels are related to the use of lead paint in those areas.
Why are lead levels higher in forests? Perhaps the soil in other areas has been supplemented or worked in ways that reduce lead. I suspect any patch of ground in Manhattan that is NOT forest has been gardened in at some point. If you add soil or compost that would certainly reduce the concentration of lead.
The stuff along the West Side waterfront doesn’t surprise me, it was heavily industrial for years (waterfront activity and then the West Side Highway, plus rail) and then sat fallow for years with no one amending or mitigating any toxins in the soil. It’s only recently the area has become fashionable!