Presentation on theme: "Lead and Other Contaminants in Baltimore Urban Garden Soils: What You Can Do to Protect Your family Rufus L. Chaney USDA-Agricultural Research Service."— Presentation transcript:
Lead and Other Contaminants in Baltimore Urban Garden Soils: What You Can Do to Protect Your family Rufus L. Chaney USDA-Agricultural Research Service Environmental Management and Byproducts Utilization Lab, Beltsville, MD Real Food Farm Education-Civic Works Workshop on Urban Soils April 16, 2014
Urban Soils and Dusts Are Contaminated Pb, Zn, Cd, As (volatile elements). – Stack emissions – Vehicle exhausts – Paint debris. – Orchard Residues (suburbs). Hg PAHs PCBs PBDEs Local Industry = local contamination variation. INDOOR Dusts Much More Important Than Soils: – Pb, Hg, PCBs, PBDEs, formaldehyde, etc.
SOIL-PLANT BARRIER Processes in soils or plants which prevent excessive food-chain transfer of elements Insolubility or adsorption in soil or plants roots: – Cr, Pb, Fe, Hg, Sn, Au, Ag, Zr, Al, F, Ti, etc. Phytotoxicity limits plant yield at levels which are not toxic for lifetime consumption by livestock: – Zn, Cu, Ni, As, Mn, B, etc. Exceptions to Soil-Plant Barrier: – Cd, Se possible risk to humans – Mo, Se, (Co) possible risk to livestock Barrier can be circumvented by direct ingestion of surface soil or biosolids: – Pb, F, Fe, Hg may comprise risk if high in soil surface.
Potential Environmental Problems From Highly Contaminated Gardens Excessive Pb absorption by children: – Hand-to-mouth transfer of housedust allows paint and soil Pb to be ingested by children. – Most important for gardens: Keep soil out of homes. – Reasonable gardening does not contribute to Pb risk. Phytotoxicity from Zn - Acidic (possibly Cu, Ni): – Only with Zn-sensitive vegetable crops. – Very low soil pH, <<5.5, unwise for gardening Excessive Cd in crops: – Highly contaminated biosolids (before regulations). – Low soil pH. High Cd/Zn ratio allow food-chain transfer. – Not known to occur in Baltimore region.
Variation in garden soil Pb concentration in Baltimore region; Left = gardens soil above median 100 mg Pb /kg; Right = gardens with soil Pb below median concentration (422 garden soils) [Mielke et al., 1983]
Metals in Baltimore Urban Gardens (Mielke et al., 1983) N=422 Pb Cd Zn Cu Ni pH mg/kg dry soil Mean S.D Min th th th th th Max Probability of clustering by chance US BkgGM
Effect of Distance from the Center of Baltimore on Pb Concentration in Garden Soils (1983). Distance N Mean Med. 90%-ile Max. %>500 km mg Pb/kg dry soil US
RISK OF SOIL/DUST Pb TO CHILDREN Some soils contain substantial levels of CaCO 3, or other alkalinity which can neutralize stomach acidity. Any process which prevents stomach acidification reduces soil Pb bioavailability. adsorption/occlusion Pb is strongly adsorbed or precipitated in soils. Reversal of specific adsorption/occlusion can be much slower than the original adsorption, a phenomenon called hysterisis. fasting Absorption of soluble Pb compounds during fasting is about 60-80%, but only 1-5% when ingested with a nutritious meal. Prolonged fasting Prolonged fasting by urban poor children may be a primary causal factor in their Pb absorption and Pb- disease compared to suburban children.
Recommended childhood blood Pb limit
Poole et al., 1980 Recommended childhood blood Pb maximum
Effect of Depth in Soil and Distance From Painted Wall on Pb in "Houseside Soil” Side of House Distance Depth A B C m cm ----mg Pb/kg dry soil
Risk from Soil Pb is through Soil Ingestion, not from Garden Foods. If Good Urban Gardening Practices are followed, garden crop Pb is increased only slightly when soil Pb is µg/g. Living in an area with soil Pb in excess of 400 (bare soil) to 1200 mg/kg (grassed soil) may increase children's blood Pb (HUD; CDC; EPA). Thus, the dominant pathway for soil Pb risk to humans is inadvertent housedust and soil ingestion by infants and children. To prevent this risk, one can move the child; remove and replace the contaminated soil; or treat the soil to reduce soil Pb bioavailability. Careful Urban Gardening Need Not Increase Pb Risk to Young Children.
James et al., 1985
Effect of Soil on Availability of Pb to Rats, and Bioavailability of Pb in Baltimore Garden Soils. TEST DIET Tibia-Pb % of Pb(OAc) 2 mg/kg ash Basal0.3 e- Basal + 5% Soil0.0 e- Basal + Pb(OAc) a100 Basal + Pb(OAc) 2 + 5% Soil130. bc53 Basal ppm Pb Soil40.0 de16 Basal ppm Pb Soil108. c44 Basal ppm Pb Soil37.1 de15 Basal ppm Pb Soil53.6 d22 Basal ppm Pb Soil173. b70 Pb added to supply 50 mg Pb/kg diet
Effect of Soil Pb and Soil Dose on Pb Absorption by Rats
Bioavailability of Soil Pb to Humans Under Fasting or Fed Condition. Results of human feeding studies with soil from the Bunker Hill Superfund Site (Maddaloni et al., 1998). Group Age Weight Pb Dose Soil Dose Bioavailability N=6 yrs kg µg mg % Fasted ( ) Fed ( )
THE URBAN SOIL LEAD ABATEMENT STUDY Sample Time Treatment Group Soil+Dust Dust Control µg/dL Pre-Abatement Mo. Post Mo. Post Effect of Replacing Soil With 1790 mg Pb/kg on Blood-Pb in 1-4 year old Boston Children with elevated Blood-Pb Levels (Weitzman et al., 1993).
THE URBAN SOIL LEAD ABATEMENT STUDY ”... suggests that lead-contaminated soil abatement is not likely to be a useful clinical intervention for the majority of urban children in the United States with low-level lead exposure.” Paint-Pb remains the most important source of Pb risk to urban children in the US. Possible that the effectiveness of the soil abatement may have been reduced because the children had been exposed to high Pb soil/dust before the abatement, and decline in Blood-Pb may not occur as rapidly as rise upon exposure. Soil containing 1790 mg Pb/kg was replaced. Blood-Pb declined µg/dL due to the independent effect of soil replacement.
In-vitro Bioavailability Extractions Spectroscopic experiments on field samples Lab scale experiments to support field results Related but different experimental ideas: Exploratory chemistry Objectives of IINERT Plots at Joplin Feeding Tests for Pb Bioavailability: Rats, Pigs, Humans
Joplin Soil Feeding Test Clinical Protocol Human volunteers with Pb isotope ratio different from that of the test soils. Screening and physical exam. Obtain informed consent. Three day clinic admission. Fasting when dosed with test soils. Subjects dosed at 250 µg Pb/70 kg BW using soil <250 µm in gelatin capsules. Collect blood and urine samples. Analyze isotope ratios using ICP-MS. QA/QC on all samples; chain of custody handling.
Joplin Soils Group Age Weight Pb Dose Soil Dose Bioavailability yr kg µg mg %, Absolute Untreated ( ) P-Treated ( ) Graziano, Maddaloni et al., 2001; unpublished. Phosphate Amendment Reduced Soil Pb Bioavailability to Humans
PHOSPHATE INACTIVATION OF SOIL Pb IN JOPLIN TEST Comparative Bioavailability Results-- Pig, Rat, Human and In vitro Method Bioavailability %-Reduction Pig (Casteel et al.)29 Rat (Hallfrisch et al.)40 Human (Graziaoni, Maddaloni et al.)69 In vitro (pH 1.5)18 In vitro (pH 2.5)69 Soil tested 18 months after H 3 PO 4 treatment in field.
Results from the Joplin field evaluation illustrate: Reduction in soil Pb, Zn and Cd phytoavailability and potential phytotoxicity. Reduction of soil Pb bioavailability to mammals (rats, pigs, human adults). Correlation of in vitro bioaccessible Pb reduction with reduction in bioavailability to test animals fed treated soils. Phosphate treatments without Fe oxides hastened formation of chloropyromorphite. Addition of P to biosolids compost or Fe Oxide increased Pb adsorption and precipitation.
Results from the Joplin field evaluation illustrate: The Drexler in vitro bioaccessible Pb extraction method did not measure Pb inactivation when the extraction was conducted at pH 1.5 or 2.0, while pH 2.2 and 2.5 results were correlated with animal tissue Pb levels. Extent of inactivation of soil Pb increased with time in the field, but not in the laboratory. – Perhaps due to poorer mixing in field soils, coupled with inhibition of reaction because both Pb and P are adsorbed strongly on particles.
ChloroPyromorphite: Does Pb Remain Non-Bioavailable? Scheckel and Ryan (2002) reacted phosphate with soluble Pb and examined the precipitate after 1 hr, 1 d, 1 wk, 1 mo, … 1yr. Examined EXAFS, XRD, and DGT properties of compounds formed; after 1 hr, no further reaction was observed. Examined dissolution in acid and found after 1 hr, rate not further reduced. In soil, extent of reaction increases with time and bioavailability only becomes lower. Reaction could occur during digestion or during bioaccessibility testing if P and Pb aremixed in soil.
In Practice, Incorporating Compost Reduces Pb Risks in Several Ways. Highest Pb is usually on soil surface. Incorporation of compost with rototiller mixes Pb with tillage depth, reducing risk from surface soil. Phosphate and Fe in compost transform soil Pb into forms with much lower bioavailability. Compost amendment supports strong growth of turfgrass, making it much more difficult to eat the soil or drag it into your house. One can measure highest Pb near house using XRF and remove that soil to landfill before incorporating compost and tilling.
Accumulation of Pb in Carrots (Codling et al., 2014) Soil Soil Pb Pb in Carrot Tissue Series Peeled Root Peel Shoots mg kg -1 dry weight----- Christiana d0.15 d0.16 c Bagstown c0.75 c2.81 b Hudson b0.97 bc2.94 b Spike c1.05 b2.37 b Cashmont a1.56 a5.07 a Bagstown, Hudson, Spike and Cashmont are old orchard soils from MD, NY, MI, and WA, respectively.
Effect of Soil Amendments on Pb Concentration in 'Tania‘ Lettuce Grown in Urban Garden Soils in a Growth Chamber (Sterrett et al., 1994) Treatment Soil Pb Concentration, mg/kg DW mg Pb/kg dry lettuce shoots---- Control2.8 a 15.7 a17.7 a 37.8 ab NPK2.0 a 3.8 ab 8.4 a 26.6 bc NPK + CaCO a 9.3 ab 6.0 a 43.7 a NPK + P2.9 a 4.4 ab10.5 a 17.2 c NPK + 5% Comp. ‡ 2.2 a 2.4 b 6.5 a 16.1 c NPK +10% Comp. ‡ 2.6 a 2.8 b 5.3 a 19.7 c ‡ Composted Biosolids rich in CaCO 3, PO 4, and Fe oxides.
Crop Selection for High Pb Soils Soil < 500 mg total Pb/kg dry weight: – Grow any crop you want; wash before cooking or eating fresh. Soil 500 to 1500 mg Pb/kg dry weight: – Limit low growing leafy vegetables (or use raised beds) No lettuce, spinach, chard, herbs (collards, kale, cabbage okay) – Limit storage root crops (potato safe if washed well) – Gardeners need to keep soil out of homes. – All other crops safe for families; wash well. Soil >1500 mg Pb/kg dry weight – If soil has low soil Pb bioaccessibility, continue cropping; Do not grow leafy and root crops. – Take extra care to keep soil out of home – Wash crops well to remove soil particles before cooking Running water; care of home cook.
Crops Differ Greatly in Pb Accumulation in Edible Plant Tissue Low growing leafy vegetables both accumulate Pb from soil, and soil-Pb is splashed onto leaves. – Lettuce, spinach, chard, herbs, etc. Root vegetables which are enlarged hypocotyls can accumulate Pb within their xylem tissue. – Carrot, beet, turnip, radish, etc. Tubers are phloem fed and very low in Pb. – Potato Fruit and Seed crops are very low in Pb even when grown in high Pb soils. Further, Pb in foods has much lower absorption by humans than assumed by EPA.
Pb Phytoextraction: Bogus If a plant is phosphate deficient, in acidic Pb-rich soil, it can take up and translocate a little Pb. A very few species an accumulate even 300 ppm Pb in acidic low P soils (Ragweed). But if the soil has enough P to give full yields, very little Pb is absorbed or translocated by any plant. There is no natural Pb-hyperaccumulator (1%) – 1% Pb in 20 t/ha biomass removes 100 ppm from soil. Adding EDTA to promote Pb dissolution and uptake causes Pb leaching to groundwater. – And 10 mmol/kg soil costs >$20,000/ha-yr. Pb Phytoextraction cannot be permitted, doesn’t work and would be very costly!
Urban Soil Bioaccessible Lead Test 1.We have tested a simplified soil Pb bioaccessibility extraction test method (extraction of 5 g of <2 mm soil with 50 mL of 0.4 M glycine·HCl solution adjusted to pH 2.5 using 4 M NaOH (= 0.38 M), at 25°; shaking for rpm) which is 8-20 times less expensive than other Pb- bioaccessibility test methods. 2.The method was designed to have high correlation with the reduction in Pb bioavailability results from feeding Joplin, MO, control and phosphate-remediated smelter contaminated soils to humans, pigs and rats. 3.When applied to Pb rich urban garden soils, the method revealed that fractional bioaccessibility (bioaccessible compared to total) of Pb in urban garden soils is only 10±2.2% of total Pb in soils containing ppm Pb, far lower than the 30% absolute bioavailability presumed by US-EPA in evaluating risk from soil Pb (IEUBK model).
Bioaccessibility of Pb in Urban Garden soils is much lower than assumed by US-EPA in the IEUBK Model
Many urban and orchard soils are enriched in Pb from historic use of leaded gasoline, Pb- pesticides, and Pb-paint - Human Activities. Among all garden crops, carrot and low-growing leafy vegetables have been found to accumulate significant levels of Pb when grown in high Pb soils (soil contamination/splash, or uptake). The Pb in carrots is within the xylem elements which run thru carrot storage roots. Other storage root crops (expanded hypocotyls) also have xylem thru the edible root and accumulate Pb (radish, redbeet, turnip, etc.) Summary: Urban Soils are Rich in Pb
Research has shown that Pb consumed with meals has much lower bioavailability (2-5%) compared to soluble Pb in water (60-80%). One feeding test with Pb absorbed in spinach shoots (with roots removed in order to get much Pb into the crop) found very lower bioavailability. The first limit on garden soil Pb concentration is to protect children from ingested soil. Depending on bioavailability of Pb in soil, the maximal soil Pb is recommended by EPA & HUD to be 400 mg/kg for bare play area soils, and 1200 mg/kg for the rest of the yard. Crop Pb Risk is Complex
Garden soils have been found to have much lower bioavailability of Pb than presumed by US-EPA when they established the 400 mg/kg guidance. EPA assumed 30% absolute Pb bioavailability for soil and housedust, while many urban garden soils with mg Pb/kg have 5-10% absolute bioavailability. The second limit is the need to limit Pb accumulation in low-growing leafy vegetables and root vegetables such as carrot, beet, turnip and radish. Fruit and seed crops remain low in Pb even on high Pb soils. Gardens Soils Have Low Pb Bioavailability
Identify previous land use and contamination sources before choosing location of garden. Analyze garden and yard soils for Pb, As, Cd and Zn levels and pH, and place garden where metals are lower – Away from houseside areas (> 1 m). If bare soil total Pb exceeds 400 mg/kg, seek analysis of bioaccessible Pb; limit exposure. Based on observed low bioavailability of Pb, and the low bioavailability of Pb in garden crops, gardeners should restrict growing of low-growing leafy vegetables and storage root crops soil Pb exceeds 400 mg/kg dry soil. Focus on keeping urban soil out of homes. Common Sense Gardening and Pb