Protocol Development for Assessing Arsenic Background Concentrations in Florida Urban Soils Tait Chirenje*, L. Q. Ma and A. G. Hornsby Soil and Water Science Department, University of Florida, Gainesville, FL 32611-0290, U.S.A. K. Portier Statistics Department, University of Florida, Gainesville, FL 32600-0339, U.S.A. W. Harris Soil and Water Science Department, University of Florida, Gainesville, FL 32611-0290, U.S.A. S. Latimer Department of Urban and Regional Planning, University of Florida, Gainesville, FL 326-5705, U.S.A. E. J. Zillioux Florida Power and Light, Environmental Services Department, PO Box 14000, Juno Beach, FL 33408, U.S.A. (Received 20 February 2001, Revised manuscript accepted 26 March 2001) Knowledge of arsenic background concentrations in urban soils is important for making remediation decisions. The soil cleanup target level (SCTL) for arsenic in Florida lies within the range of arsenic background concentrations. The residential SCTL is also near the practical quanti®cation limits using analytical procedures. Currently no standard protocols are available for determining arsenic background concentrations in urban soils, apart from site-speci®c cases. Therefore, a pilot study was conducted to develop and employ appropriate protocols to determine arsenic distribution in urban soils. This involved: site selection (e.g. size and sampling frame), sample collection (e.g. sampling technique), and statistical considerations (e.g. design). Factors such as ease of sample collection and maintaining anonymity of private properties were also considered as they in¯uence the successful implementation of the study. Forty surface soil samples each were collected from ®ve categories in three land use classes (residential-yard and right-of-way, commercial and public land-parks and public building), digested using EPA method 3051a and analysed using graphite furnace atomic absorption spectrometry. Experiences from the pilot study (e.g. complications during sample selection, digestion, data censoring etc.) were used in the development of the ®nal protocol to be used in determining the distribution of arsenic in urban areas. # 2001 AEHS Keywords: anthropogenic; background; urban soils; strati®cation. Knowing background concentrations of arsenic in urban soils provides a yardstick against which the impacts of human activity can be measured. Back- ground concentrations of arsenic in relatively undis- turbed Florida soils are established and they vary from 0.01 to 61.1 mg/kg, with a geometric mean (GM) of 0.27 mg/kg (Chen, Ma and Harris, 1999). Typical soil arsenic concentrations range between 0.1 and 40 mg/kg worldwide, with an arithmetic mean concentration of 5±6 mg/kg (Kabata-Pendias and Pendias, 1992). How- ever, little information is available on arsenic back- ground concentrations in urban soils. Urban soils, created and/or modi®ed in the process of urbanization, are complex and hetero- geneous in their structure and composition (Craul, 1985; Davies, Watt and Thornton, 1987). In contrast to natural agents such as wind, water, ice, gravity and heat, human activity is the predominant active agent in the modi®cation of these soils (Barrett, 1987). There is a higher probability of historic anthropo- genic contamination, vertical mixing during develop- ment, use of ®ll from dierent geologic areas, deposition and/or contributions from the use of pesticides or amendments from other sources in urban soils than in undeveloped areas (Craul, 1985; Thornton, 1987). 141 1527-5922/01/020141+13 $35.00/00 # 2001 AEHS Environmental Forensics (2001) 2, 141±153 doi:10.1006/enfo.2001.0046, available online at http://www.idealibrary.com on *Fax: 352 392 3902. E-mail: tchirenj@u¯.edu