Given the fact that I had posted a previous article on lead in urban gardens, it seemed fitting to create this as a follow-up.

I believe Washington D.C. is considered an urban environment

The White House Goes Green!

In case you missed it, First Lady Michelle Obama (with the help of staff and local students) broke ground and planted an organic fruit and vegetable garden on the White House lawn earlier this year.  The “fruits” (or should I say vegetables) of their labor started to be harvested and June with the intent to provide fresh, organically-grown produce for the First Family, White House staffers and even some State dinners!

See the video below for an up close look at the White House gardening venture:

Amongst all the initial hoopla associated with the planting of the garden was a report of “elevated” levels of lead in the soil of the garden plot.  According to a story in today’s New York Times, the initial level of lead reported was 93 p.p.m. which is less than 25% of the hazard level established by the U.S. E.P.A. (though countries like the Netherlands set hazard levels as low as 40 p.p.m.).

Through the actions taken to enhance the productivity of the garden plot, lead levels were decreased to as low as 14 p.p.m. Concentrations like these are typically found in areas where there has been little human activity and is indicative of natural levels of lead in the environment.

So what actions were taken exactly?

A few simple organic gardening steps were implemented to enhance the ground’s fertility and also reduce the availability of lead to the plants including:

• Addition of lime;
• Addition of green sand;
• Addition of crab meal;
• Addition of organic compost supplied by the National Park Service; and
• Adjusting the soil pH to between 6.5 and 7.

It should be noted, when developing compost to use in produce gardens be sure to avoid using organic material obtained along roadways or in high traffic areas since this material often has higher levels of lead.

So the next time your near D.C. and pass the organic produce section of a local market, think about the steps taken at the White House to produce contaminant-free and nutrient-rich fruits and veggies.  On the other hand, if the produce was grown on another urban garden, hopefully they used similar practices to “keep the lead out”.

Many of us are also re-cultivating, fertilizing (organically-based of course) and preparing to plant another season’s crop of home-grown wholesome vegetable bounty from our backyard gardens.

So why even consider the idea that lead poisoning could weigh-down summer urban gardening plans?

If you have a large lot, live in a relatively new development or in a structure that has never used exterior paint you may not even have to think about the significance of this article’s title.

One the other hand, if you live in an older structure, particularly in an urban or suburban setting, you really should be doing more than thinking about the title.

The reason: until the 1978 Lead Paint Ban many homes were painted using lead-based paints. As structures aged and maintenance painting occurs, some or all of the original paint was removed via scraping and the paint chips fell to the ground below and became part of the soil.

Another lead source present until the mid-1970s was the presence of tetra-ethyl lead in gasoline when it was phased out of product and replaced with other additives such as methyl tertiary butyl ether (a.k.a. – MTBE: a subject for a future post).  As particulate matter was deposited from automobile exhaust, it also contained a certain amount of lead from gasoline adding to the lead burden of shallow soils (also the places where gardens are grown).

Lead in the Urban Garden Soil Environment …

First of all, if you feel your property may have significant issues with lead in soil, you should consider contacting your local/state health or environmental department for more information and testing advice.  This article is posted for those interested in gardening and is searching for steps to take to minimize interaction between garden plants and lead contaminated soils.

Lead is present in all soils in relatively low concentrations (often < 20 mg/kg or ppm), which represents a minimal risk to plants or animals (including us) that come into contact with it.

The problem arise when lead soil levels become substantially increased, a common occurrence in urban and some suburban setting due to the reasons stated above.  In numerous urban/suburban cases, lead concentrations in residential soils greatly exceed the common “lead safe” soil standard (established by U.S. regulatory agencies) of 400 mg/kg (ppm) with some studies reporting soil lead levels 10X greater than the safe level.

Note: Even though the “safe-lead” standard is set at 400 mg/kg (ppm), cultivation of soils with soil lead levels > 100 mg/kg (ppm) should be avoided when children at present to lower the risk of direct ingestion of contaminated soils.

Do vegetation types uptake and accumulate lead in the same way?

According to studies on the uptake of lead by different types of garden plants, leafy (lettuce, herbs, rhubarb, etc.) and rooting (carrots, radishes, onions, etc.) edible plants are more likely to accumulate lead in the edible parts than fruiting edibles (tomatoes, peppers, squashes, etc.).

A few recommendations for urban gardeners:

1. Survey the property and plan to construct the garden away from high contamination areas and buildings;
2. Conduct analysis of soil samples from planned garden area;
3. If planned garden area contains > 400 mg/kg (ppm), either move location, switch to container or raised bed gardening;
4. If lead contamination is present, only grow leafy and rooting plants in container or raised bed systems;
5. Wash all harvested plants thoroughly to remove contaminated dust/soil;
6. Each season, re-check topsoil system to check for re-contamination during pre-season preparation activities;
7. Do not use plants grown on contaminated soils in composting efforts.

A little pre-planning and preparation before undertaking this season’s gardening endeavor will help lower the risk of lead exposure to your family and still provide fresh, great-tasting and wholesome fruits and vegetables we all relish!

The added bonus – you will minimize the potential for lead poisoning to weigh down your urban garden plans!