It’s A Dirty Business

Among its many other services, Penn State Extension service offers soil testing. The extension service will tell you which crops will grow well in your soil and what you’d need to add for specific crops. They will also test for a number of toxic metals and other details.

Many people in Garden City have gardens – and some chickens. This recent article about backyard chickens in Australia prompted my interest in soil testing. I thought it’d be worthwhile to have the soil here tested to find out if its safe to garden in. Many urban areas have extensive pollution from past industries and the remnants of leaded gasoline. Nether Providence was a mill town at one point, but instead of industrializing further, it ended up becoming a suburb community of Media and Chester (and later Philadelphia).

Our soil pH was 6.3, a little low, and potassium and magnesium were 200 and 231 ppm, a little high. Phosphorous was 44 ppm, in the optimum range according to the report. Of the regular (non-toxic) metals the extension service tests for, zinc was 14.2, copper 4.1 and sulfur 15.1. The zinc is above the normal range, but the other two within the expected range listed and fine for growing.

The toxic metals test took an extra week to come back. The results were:

  • Arsenic 5.76 mg/kg
  • Mercury 0.099 mg/kg
  • Lead 82.60 mg/kg
  • Selenium <1.25 mg/kg

Arsenic is a naturally occurring toxic metal. Doses of 60,000 micrograms are fatal, and lower doses consumed over long periods can cause a variety of ailments. The EPA states that arsenic levels in soil are usually 0.1 to 40 mg/kg while the article linked above sets the safe range to between 5 and 20 ppm, and our test lays in the low end of that. You’d need to eat 12 kg of soil to receive a fatal dose of arsenic in one sitting, so I wouldn’t recommend that.

Mercury is a toxic metal produced by a variety of industries, and causes numerous health issues depending on the chemical form. The North Carolina State extension states the average background level of mercury in soil there is 0.060 ppm. New York’s guideline for mercury in residential soil is 0.81 ppm. While slightly above average, our soil is an order of magnitude below New York’s cutoff for concern.

Lead is a heavy metal known to cause a variety of ailments, particularly for children. Soil naturally contains about 50 mg/kg of lead, but the extension service classifies less than 150 mg/kg as very low. In an urban area, this is considered low and the extension service does not recommend taking actions.

Unlike the other metals tested, selenium is not outright toxic. While harmful in high doses, you can buy nutritional supplements containing it and it apparently has some health benefits. But in high doses, above 400 micrograms/day its harmful. Our measurement was too low for the extension service’s test so toxic build up of selenium in our plants are unlikely.

So good news, most of Garden City should be safe for gardens and chickens and children can play in the dirt. The one potential concern might be lead paint in your particular house. Many of the houses here were built at a time lead paint was common, so it may remain in the soil near the house. The county has a lead testing program, but homes in Garden City are unlikely to qualify. This document contains contact information for lead testing companies in the area (at the bottom of the pdf) if you’re concerned.

Categories: Ramblings