Download Healthy practices for metals in soil

Healthy Gardening Practices for Metals and
other Common Garden Contaminants
Pukhraj Deol
Metro Master Gardener Recertification Training
Thanks to Linda Brewer for slide and photo contributions!
Nov 12, 2016
Could my current or future garden location be
impacted by historic contamination? How?
what activities took place at the garden location that could have
impacted the soil.
• Farming/agriculture (pesticides, herbicides, metals)
• Residence (lead-based paint, petroleum from tanks)
• Commercial – auto repair shop or dry cleaner (petroleum,
metals, chlorinated solvents)
Understanding Heavy Metals in Soil
• How metals behave in soil
-not mobile
• Why it’s important to test
• Collecting soil samples and
interpreting test results
How metals behave in soil and plants
• Mobility- do not move much in soil except when soil manually disturbed
• Do not use top soil of unknown quality in your garden
• Plants preferably uptake essential nutrients
• Most plants when grown in fertile, well-managed soils do not uptake heavy
metal contaminants
• Not all heavy metals are toxic
• Some metals are essential plant nutrients e.g. Fe, Zn and Cu
• Commonly found form of Cr (trivalent) is less toxic than hexavalent Cr
Plants grown in fertile soils do not easily uptake heavy metals
• Availability and uptake depends on soil fertility and pH: avoid nutrient deficiency and manage pH
http://cwmi.css.cornell.edu/Metals_urban_garden_veg.pdf
Uptake varies by plant species
• Some crops like blueberry need more Fe
• Some special plants have capability to
uptake heavy but it requires a lot of
manipulation to make these plants
accumulate significant amounts of heavy
metals
• Examples: Indian mustard, alfalfa, cabbage,
tall fescue, juniper, and poplar trees
https://www.kelatox.com/content/images/cadium.jpg
Why it’s important to test soil
• Safely grow edibles
• If you suspect heavy metal
pollution based on site history
• Site history unknown
• No need for testing if using raised
beds filled with good quality soil
mix (e.g. from Natures
needs/Recology)
Collecting soil samples
• Remove surface mulch/organic matter layer
• Collect samples where you plan to plant edibles
• Multiple subsamples, mix and take representative
sample
• Sampling depth
• Test for heavy metals: top 2 inches (metals are
not mobile)
• General soil test for knowing fertilizer and lime
need – 6inches
Screening level comparison (units mg/kg or ppm)
Safe Gardening Practices
when Metals are an Issue
1. Grow in raised beds or
containers. Use clean
planting mix.
2. Mulch barrier between
kids and contaminated soil;
reduces dust and bare spots.
Safe Gardening Practices
3. Apply compost or organic
material to annual plantings
4. Avoid soil splash when
watering.
5. Amend soils for vigorous
growth and good pH.
6. Practice Good Garden Hygiene
Wash produce
Wash hands
Wear gloves and
shoes
Keep dust and dirt
outside
Garden According to Soil Test Results for Metals
Soil total lead test
results (ppm)
< 50=Background level
50-400
400-1200
>1200
EPA Recommendation
No special gardening precautions.
Grow any vegetables. Limit children’s exposure to dust
(mulch, sod) or soil consumption.
No leafy vegetables or root crops. Limit children’s
exposure to dust (mulch, sod) or soil consumption.
Plant perennial shrubs, groundcover, grass, or mulch.
Grow vegetables in uncontaminated mix in containers or
raised beds.
Whenever metals are an issue,
Which garden produce is safe to eat?1
Very Little Risk
Fruits – they follow a flower:
•
•
•
•
Tomato, pepper, tomatillo, eggplant, beans
Blueberry, kiwi, raspberry, blackberry
Cucumber, squash, pumpkin, zucchini
Apple, pear, peach, plum
Leaves:
• Kale, onion, garlic
• Annual herbs: basil, cilantro, parsley
• Perennial herbs: rosemary, sage, lavender, thyme
Buds, flowers, shoots:
• Corn
• Squash blossoms
Roots – very little risk – phloem fed:
• Potato, Jerusalem artichokes
• Kohlrabi
Less Safe
Fruits – low growing, soil splash:
• Strawberry
Leaves – difficult to wash:
• Lettuce, spinach,
• Mustard, chard, Chinese cabbage
Buds, flowers, shoots – hard to wash:
•
•
•
Broccoli
Cauliflower
Asparagus
Roots – can concentrate lead – xylem fed:
• Carrot, parsnip
• Turnip, rutabaga
• Radish, celeriac
1Provided
it is WELL WASHED.
Metal Test for Garden Produce
3
1
Average water content of common vegetables
Lettuce, cucumber, zucchini ~95% water
Beet, rutabaga, broccoli, carrot ~89% water
ppm = mg/kg
USDA National Nutrient Database for Standard Reference
Release 28
2
Division rules:
• Divide by a large number, get a small number.
• Divide by a small number, get a large number.
Examples:
400/200 = 2
400/100 = 4
400/ 50 = 8
400/(1/2) = 800
Concentrations expressed as
5
Food we eat
Test results
mg of metal/kg whole produce
mg of metal/kg dried produce
same amount of metal
amount of metal
Water lost to
heat.
4
Good gardening practices
promote robust plant
growth. MORE KG in the
denominator!
6
7
As water is driven off, the
apparent metal content of
garden produce is exaggerated!
Reconstitute Your Produce!
Optional Dreaded Story Problem
FRESH WEIGHT LETTUCE
20 ppm =
20 mg Pb
1 kg Lettuce
DRY WEIGHT LETTUCE
Drying Process
20 mg Pb
1 kg Lettuce (1.0-0.95)
20 mg Pb
= 400 ppm
0.05 kg Lettuce
DRY WEIGHT BEETS
x mg Pb
= 400 ppm
1 kg Beet (1.0-0.89)
x mg Pb
0.11 kg Beet
= 400 ppm
Drying Process
Linda sends 1 kg of beets
(89% H20) for analysis and
gets results
of 400 ppm. What was the
concentration of lead in
the fresh beets?
WET WEIGHT BEETS
x mg Pb = 400 ppm X 0.11 kg Beet
x mg Pb = 400 mg/kg X 0.11 kg Beet
x mg Pb = 44 mg
44 mg Pb
1 kg Beet
= 44 ppm
Health Considerations - Dermal Exposure
• Metals don’t absorb through our skin
ENVIRONMENTAL HEALTH
Public Health Division
18
Health Considerations - Oral Exposure
• Heavy metals in soil are only a risk when swallowed. They don’t
absorb through skin, and even in dusty, windy conditions, the
particle sizes of dust/dirt stirred up into the air are too large for us to
breath into our lungs.
• However… Most metals are not very bioavailable – Only a small
fraction (<5%) of total metals from soil or plants eaten by people are
absorbed when swallowed. Most metals pass through our bodies
quickly.
• There are currently No National Standards for the “safe” or
“healthy” level of metals in food crops.
– OHA refers to levels established for the metals in food in the World
Health Organization Codex Alimentarius (WHO Codex)
– The Codex assumes 100% bioavailablity in setting their standards
– Contact OHA for assistance with interpretation 971-673-0977
ENVIRONMENTAL HEALTH
Public Health Division
19