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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