LeadIn(g) the Way
Introduction and relevance: In the fall of 2015, I collaborated with Danielle (the founder of this website) on a Chemical Analysis project examining lead—hence the pun in the title—in soil from community gardens. We examined soil samples from the Bowdoin Organic Garden (BOG) in Brunswick, ME and from the Clinton Community Garden (CCG) in NYC, NY. These gardens weren’t randomly chosen; the BOG is accessible and very prevalent in Bowdoin students’ lives, and the CCG is Danielle’s hometown garden with a history of high lead concentration. Lead, a heavy metal, is a common environmental contaminant that can cause damaging health effects. It’s a possible carcinogen and especially a concern for children, as studies have linked lead exposure to cognitive and behavioral complications1. Much of the produce from these gardens end up on dinner plates, so the results of this research are important. It’s hard to predict how much lead will end up in the plants grown in lead-contaminated soil, but there is a correlation between high lead concentration in soil and more lead detected on crops 2.
For some context on values: The New York State Department of Environmental Conservation (NYS DEC) listed 18.7 ppm as a background level of lead in soil; there is no definitive “safe” amount of lead in soil, though the NYS DEC uses 400 ppm of lead as a starting point for a hazardous amount to consume, inhale, and eat vegetables grown in the soil. In 1994, the CCG was reported to have 500 ppm of lead! We inferred that was because the garden used to be a junk lot with old buildings using lead paint.
Project goals: the main goal was to determine how much lead was in the soil samples we collected. We were also interested in seeing if these amounts were safe and if there was a statistically significant difference between the values we found.
Experiment summary: I don’t want to bore you with exactly how we collected and analyzed our samples, so I’ll be as brief as possible. We collected samples from random parts of the gardens (Danielle’s mom helped by getting us samples from the CCG) and used an instrument called an inductively coupled plasma (ICP) optical emission spectrometry (OES) to find the amounts of lead.
The ICP-OES runs a liquid sample through an extremely tiny tube, so we have to “digest” the soil, which means we put strong acid in it and dissolve everything using a really powerful microwave. Not everything would dissolve and we don’t want to clog to the instrument, so before the digestion process, we picked out matter like rocks, twigs, and even a worm. Once we had only liquid sample (clear at this point since we only wanted dissolved material, so nothing should have been floating around), the ICP-OES heated the minerals in there (like lead) to the temperature of the sun. This excites the minerals, which produces a signal that tells us what it is (elements produce specific signals, so we could tell lead from copper) and how much of it is in there (through intensity of the signal).
This instrument was best because it can accurately single out the lead. We checked our technique by measuring known lead amounts in standards prepared with same method. From our “checking,” we did well, meaning our method was pretty good!
What we found: The CCG sample (using four replicates of a composite sample, which means we combined random samples into one and tested that four times) was 185 ± 14 ppm, and the BOG sample (also four replicates of a composite sample) was 28 ± 2 ppm. Statistical analysis (a t-test, which is a way to compare the two means) showed they were significantly different.
What this means: Our results show that the soil is considered safe by the NYSDEC! And that there was definitely more lead found in the soil from the CCG, which makes sense because of its history. We hypothesize that the higher amount was due to environmental differences; NYC is a highly trafficked urban environment, while Brunswick is a less-densely populated suburban environment.
Of course, we’re not really sure how representative these values are, but they’re probably not too far off.
Also, I can’t write this without thanking our professor Beth Stemmler and lab instructor Bev DeCoster for all their help! And obviously Danielle was a great partner; she actually LEAD me to seriously think about environmental chemistry. They’re awesome, and I am so inspired by them.
Post-project thoughts: What a great experience! I think this project made data more valuable to me. It’s so easy to take for granted the values that news sources put out for us, but there’s a lot more to getting numbers than just waiting for a computer to spit out numbers at you. This project also touches upon contamination and waste, which I had never thought too much about before this class. But it’s so relevant! Chemicals aren’t inherently bad; amounts (and effects) are what’s important, so we need research to understand and collect this information.
Author Bio: Karen is a junior at Bowdoin College majoring in Chemistry with the hopes of a career in pharmacy. Though she enjoys it, research is not her passion. But community outreach and science are, so when Danielle presented her with this opportunity to combine those two, she had to take it (and she also wanted to help out her friend). The research she writes about comes from projects she’s done for classes at Bowdoin. Specifically, this project was completed for Chem 2100 (Analytical Chemistry), under the guidance of Professor Elizabeth Stemmler and Lab Instructor Beverly DeCoster. Karen also enjoys participating in Bowdoin’s Varsity Women’s Golf Team, reading young adult novels, editing usually non-serious videos, and hiking in her home state of Hawaii. Pronouns: she/her/hers.
- Goyer, R. A., Lead toxicity: current concerns. Environmental Health Perspectives 1993, 100, 177-187.
- Fytianos, K., Accumulation of Heavy Metals in Vegetables Grown in an Industrial Area in Relation to Soil. Bulletin of environmental contamination and toxicology 2001, 67 (3), 423-430.