Heavy Metals in the Environment Effect of Biosolids Processing on Lead Bioavailability in an Urban Soil Sally Brown,* Rufus L. Chaney, Judith G. Hallfrisch, and Qi Xue ABSTRACT scrofa) as well as weanling rats (Rattus spp.) as human surrogates, have shown that the mineral form of Pb, fed The potential for biosolids products to reduce Pb availability in both in a soil matrix and as pure minerals, can alter soil was tested on a high Pb urban soil with biosolids from a treatment plant that used different processing technologies. High Fe biosolids the rate of Pb adsorption (Baltrop and Meek, 1975 compost and high Fe lime biosolids compost from other treatment Freeman et al., 1996 Ruby et al., 1999). Lead bioavail- plants were also tested. Amendments were added to a Pb-contami- ability to immature swine from 19 untreated substrates nated soil (2000 mg kg 1 Pb) at 100 g kg 1 soil and incubated for 30 collected from 8 sites ranged from 0.01 to 90% (Casteel d. Reductions in Pb bioavailability were evaluated with both in vivo et al., 1996a���d, 1997, 1998a���c). Differences in Pb bio- and in vitro procedures. The in vivo study entailed feeding a mixture availability were attributed to the presence of different of the Pb-contaminated soil and AIN93G Basal Mix to weanling rats. mineral species using an in vitro procedure (Medlin, Three variations of an in vitro procedure were performed as well as 1995). These results suggest that lead bioavailability in conventional soil extracts [diethylenetriaminepentaacetic acid (DTPA) soils can be manipulated by changing its mineralogy. and Ca(NO3)2] and sequential extraction. Addition of the high Fe Currently, removal and replacement of contaminated compost reduced the bioavailability of soil Pb (in both in vivo and in vitro studies) by 37 and 43%, respectively. Three of the four compost soils is the most commonly used remedial option for materials tested reduced Pb bioavailability more than 20%. The rapid high Pb soils (Berti and Cunningham, 1997). Removal in vitro (pH 2.3) data had the best correlation with the in vivo bone and replacement is not economically or environmentally results (R 0.9). In the sequential extract, changes in partitioning feasible to carry out in high density urban areas. Re- of Pb to Fe and Mn oxide fractions appeared to reflect the changes search to limit the bioavailibility of Pb in situ has focused in in vivo Pb bioavailability. Conventional extracts showed no changes on the addition of soil amendments to alter the Pb in metal availability. These results indicate that addition of 100 g chemistry in place. Much of this work has focused on kg 1 of high Fe and Mn biosolids composts effectively reduced Pb the formation of pyromorphite through the addition of availability in a high Pb urban soil. P amendments (Cotter-Howells and Caporn, 1996 Ma et al., 1995 Pearson et al., 2000). While P addition has been shown to be effective, there are environmental Ingestion of lead-contaminated soils is one of the concerns related to high rates of P amendments, such primary factors responsible for elevated blood Pb in as the potential for increased eutrophication in adjacent children (Mielke, 1999). Although incidences of blood water bodies (Sharpley and Beegle, 1999). Pb above the current guideline of 10 g dL 1 have Other amendments have also demonstrated the abil- generally decreased, occurrences of elevated blood Pb ity to reduce Pb bioavailability. The addition of manga- are still common in urban areas. In 1988, the Agency nese along with P to soil has reduced both in vivo and for Toxic Substances and Disease Registry estimated in vitro Pb availability over the addition of P alone or that more than 3 million children ages 6 mo to 5 yr living Mn alone (Hettiarachchi et al., 2000). The addition of in metropolitan areas had blood lead levels greater than ���iron rich��� material, a high Fe by-product from titanium 15 g dL 1 (Agency for Toxic Substances and Disease processing, reduced in vitro extractable Pb in several Registry, 1988). The report also stated that soil Pb con- Pb-contaminated soils (Berti and Cunningham, 1997). centrations greater than 500 to 1000 mg kg 1 were asso- The importance of soil organic matter in limiting Pb ciated with increased child blood Pb. Median concentra- availability has also been demonstrated (Strawn and tions of Pb in inner city soils are greater than 1000 mg Sparks, 2000). The application of biosolids materials kg 1, suggesting that elevated Pb in soils is at least par- (by-product of municipal wastewater treatment) may tially responsible for the observed elevated blood Pb in offer an alternative option. Recent studies indicate that children living in urban areas (Angle et al., 1974). application of biosolids or biosolids compost can reduce The relationship between the mineral form of Pb and the bioavailability of soil Pb (Brown and Chaney, 1997 its bioavailability has been demonstrated in in vivo and Brown et al., 1999). This is reasonable, given that biosol- in vitro trials. Feeding studies, with immature swine (Sus ids often have high concentrations of Fe and P (g kg 1) and Mn (mg kg 1), and generally contain 50% or- S. Brown, College of Forest Resources, Box 352100, Univ. of Washing- ganic matter. ton, Seattle, WA 98195. R.L. Chaney, Animal Manure and By-Prod- ucts Laboratory, USDA ARS ARNI, Beltsville, MD 20705. J.G. Hall- While the addition of P to Pb-contaminated soils has frisch and Q. Xue, Diet and Human Performance Laboratory, USDA ARS HNRS, Beltsville, MD 20705. Received 6 Sept. 2001. *Corre- Abbreviations: AAS, atomic adsorption spectrometry DTPA, dieth- sponding author (slb@u.washington.edu). ylenetriaminepentaacetic acid PBET, physiologically based extrac- tion test. Published in J. Environ. Qual. 32:100���108 (2003). 100

BROWN ET AL.: BIOSOLIDS EFFECTS ON LEAD BIOAVAILABILITY 101 a quantifiable endpoint (formation of pyromorphite), ate the importance of (i) stabilization through the com- posting process, (ii) the role of calcium carbonate, and the mechanisms responsible for the observed reduction in Pb availability in Fe-, Mn-, or biosolids-amended soils (iii) the importance of inorganic oxides in reducing Pb availability. Changes in Pb bioavailability were assessed are not clear. It is generally thought that the adsorption reaction, potentially leading to precipitation, is responsi- through in vivo (using weanling rats) as well as in vitro procedures. In addition, agronomic soil extracts were ble for the observed decrease in Pb bioavailability. Bio- solids contain high levels of organic matter and P that used to determine whether potential changes in bioavai- lable Pb would be reflected in the extractable pool of may contribute to the observed ability to limit metal solubility (Li et al., 2000). In addition, biosolids gener- this metal. ally contain high concentrations of Fe and Mn. In some cases Fe is added to biosolids in percent concentrations MATERIALS AND METHODS to aid in dewatering. The alternating aerobic and anaer- Soil and Amendment Characteristics obic conditions in wastewater treatment plants com- bined with the high organic matter and Fe content of Soils Collection, Preparation, and Analysis biosolids suggest that the formation of ferrihydrite is Soil for the study was collected from a home garden in favored and the crystallization of this oxide may be Baltimore, MD. The garden had been identified as containing inhibited. Ferrihydrite has been shown to form surface high soil Pb by the Kennedy Krieger Foundation (engaged in inner sphere complexes with Pb (Scheinost et al., 2001). helping children with undue Pb absorption in Baltimore, MD). Over time, as this oxide is aged, surface adsorption may There was no history of Pb smelting, refining, or battery recy- lead to precipitation of a more crystalline, Pb-bearing cling in the neighborhood where the soil was collected. Ap- Fe oxide. proximately 40 kg of soil was collected (top 10 cm) from Characteristics of biosolids vary depending on the garden that was immediately adjacent to the house. Soil was air-dried and sieved through a 2-mm stainless steel sieve. The stabilization process used to meet standards for patho- soil was analyzed for total carbon and nitrogen by combustion gen reduction prior to land application. Biosolids can (25 and 1.6 g kg 1). Particle size analysis with the hydrometer be treated with slaked lime for dewatering and pathogen method (American Society for Testing and Materials, 1985) reduction. Use of this material can result in increased classified this soil as loamy sand. Cation exchange capacity of soil pH. This is often desirable since increased soil pH the soil was measured as 14.7 cmolc kg 1 (Chapman, 1965). is associated with decreased metal phytoavailability. The soil and soil amendments were analyzed for total metal While the observed decrease in plant uptake of metals concentrations with the aqua regia procedure and the filtrate may not correspond to a similar decrease in bioavailabil- was analyzed with flame atomic adsorption spectrometry ity to animals, it may be that a high lime material would (AAS) with deuterium background as appropriate (McGrath neutralize the acidity in the gastric system and limit the and Cunliffe, 1985 Table 1). The source of high soil Zn (977 mg kg 1) was not clear. All other elements were within normal amount of Pb that comes into solution. Composting range for soils (Brady and Weil, 2002). Carbon, N, and P biosolids (done to produce a material that can be used concentrations were not indicative of excessive fertilization without restrictions) results in the transformation of or mulching. organic compounds to a higher fraction of humic and fulvic acids. As discussed, each of these components Biosolids Amendments may also contribute to the biosolids��� ability to limit metal bioaccessibility. By understanding the unique Biosolids amendments for the study were generated at the qualities of different biosolids products, it may be possi- Onondaga County Drainage and Sanitation Department���s wastewater treatment facility in Syracuse, NY. Biosolids from ble to maximize in situ reductions in bioavailability by the New York facility are a combination of primary and sec- applying biosolids with particular characteristics. In ad- ondary sludges that are anaerobically digested and then dewa- dition, reduction of Pb bioavailability, through the appli- tered with a belt press to achieve a solids content of approxi- cation of biosolids or biosolids products, may offer an mately 220 g kg 1 (22%). New York biosolids materials tested economically feasible alternative to current remediation included digested raw, digested and dewatered, ashed, N technologies for Pb-contaminated urban areas. VIRO (N-Viro, Toledo, OH) (heat-pasteurized through addi- This study was conducted to determine the effects of tion of slaked lime), and composted biosolids (Richards et al., different biosolids processing methods on the ability 1997). In addition to the compost produced at the Syracuse of biosolids to reduce Pb availability in an urban soil. POTW, compost (90%) lime [10% Ca(OH)2], high Fe com- post (Back River POTW, Baltimore), and compost lime Biosolids products were selected for the study to evalu- Table 1. Total metal concentrations of the high Pb urban soil and the biosolids amendments used. The soil was 2.53% C and 0.16% N. Treatment Zn Cd P Cu Mn Ca Pb Fe mg kg 1 Soil 977 0.5 795 54 418 7 574 2 135 26 900 Raw 613 8.7 29 590 542 334 45 870 135 68 100 Pellet 640 9.3 28 420 560 333 40 530 158 67 500 Ash 980 11 34 080 1 009 689 84 670 145 86 750 N VIRO 180 3.2 9 600 139 280 338 100 94 17 000 Compost 468 5.3 21 630 359 458 31 810 134 49 600 High Fe compost 800 10.8 27 390 348 867 29 560 240 99 000 High Fe compost lime 320 3.4 14 610 185 1 557 164 410 135 58 900