Regulation of Heavy Metals in Fertilizer: The Current State of

Chapter 5

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Regulation of Heavy Metals in Fertilizer: The Current State of Analytical Methodology 1

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Peter F. Kane, William L. Hall, Jr. , and David W. Averitt 1

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Department of Biochemistry, Purdue University, West Lafayette, I N 47907-1154 I M C Global, 3095 Country Road 640 West, Mulberry, FL 33860-2000

There is a trend toward regulation of non nutritive trace elements in fertilizers. The Association of American Plant Food Control Officials has developed proposed regulatory limits for A s , Cd, Co, Pb, Hg, M o , Ni, Se, and Zn. Several states are monitoring trace metals, others are considering programs. To begin evaluation of available methodology supporting such regulation, 29 labs participated in a sample exchange designed to estimate the degree of accuracy and precision possible by laboratories routinely monitoring trace metal content of fertilizer materials. Survey samples consisted of diluted solutions of certified stock standards of known concentration, and actual fertilizer materials. Laboratories used several acid digestion procedures for sample preparation, and a range of instrumentation for detection. Analytical results illustrate a lack of reasonable precision and accuracy, needed for reliable regulatory oversight. Method development activities to address these deficiencies are suggested.

© 2004 American Chemical Society In Environmental Impact of Fertilizer on Soil and Water; Hall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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Introduction In 1997 the Seattle Times published a series of articles entitled "Fear in the Fields" (7) which focused the public's attention on the practice of recycling industrial waste into fertilizer products. The series raised public concern over whether potentially harmful metals could get into our soils and plants by this practice. A book entitled "Fateful Harvest" (2), based on the newspaper series, was published by the same author. In light of these concerns, federal and state agencies responsible for regulation of fertilizer products in the United States are evaluating risks and considering the appropriate response in the public interest. Since there is merit in having relatively uniform rules and regulations related to fertilizers among various states, the Association of American Plant Food Control Officials (AAPFCO) early in 2001 approved Statement of Uniform Interpretation and Policy #25 (5). SUIP25 sets suggested upper limits of contaminant metals elements, based on a sliding scale of how much phosphorus and nutritive trace elements are claimed on the product label. Ultimately these calculations are based on formal risk assessment (4). As various states consider their regulatory options, it remains to be seen how closely they might follow the SUIP25 guidelines. Whether in uniform fashion or not however, states do seem to be migrating in the direction of additional regulatory control. Currently three states are regulating various non nutritive trace elements, Washington, California, and Texas. According to a recent survey of state regulatory agencies, conducted by the authors with A A P F C O ' s help, 21 additional states either are, or sometime this year will be, monitoring at least some non nutritive trace elements in the fertilizer products they regulate. The states are Alabama, Arizona, Delaware, Florida, Idaho, Indiana, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, New Hampshire, New Jersey, New York, Oregon, Pennsylvania, South Carolina, Utah, Vermont, and Wisconsin. "Monitoring" implies analysis of fertilizers, but may or may not imply regulation based on that analysis. This survey also asked the regulatory agencies to indicate what analytical methods are, or will be, used for existing or anticipated analysis of potentially harmful metals in fertilizers. Responses from some states were quite specific. Washington regulates 9 elements, and the methodology it specifies is E P A 3050B, and E P A 7470A/7471A for mercury. California regulates 3 elements, plus 6 more anticipated, and specifies E P A 3050B or 3051A. Texas regulates 9 elements by in house methodologies. (EPA methodologies can be found on the E P A web site at EPA.gov.) A number of other states were not as specific in

In Environmental Impact of Fertilizer on Soil and Water; Hall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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designating methodologies to use however. Responses ranged from " A O A C heavy metals methods" (even though none exist for fertilizers), to " E P A " , or the respondent wasn't sure, or methodologies were still to be determined. It should be realized that there are multiple E P A methods, http:// www.epa.gov/epaoswer/hazwaste/test/3xxx.htm, which can give varying results, and in addition, those methods are not intended specifically for fertilizer materials. E P A 3050B and EPA3051A are the most commonly referenced methods. E P A 3050B is a hotplate digestion with nitric acid, or sometimes nitric acid plus hydrochloric acid, depending on the elements of interest, and the type of instrumentation anticipated for use in the determination step. E P A 3051A uses a microwave rather than a hot plate. It may or may not match results from 3050B depending on digestion conditions, acids used, and the sample matrix. 3050B and 3051A were developed for use with sediment, sludge, and soil materials, not fertilizer materials, and their applicability to fertilizers has not been systematically investigated. Also, 3050B and 3051A are not intended to recover all of a given element from samples. They are intended to be leach methods to analyze samples from, for example, a superfund site. When using the methods, it is assumed that i f a given environmental sample does not completely digest in the nitric acid, it is unlikely the undigested portion would have potential to leach into the ground water and escape the site. E P A 3052, using hydrofluoric acid, is a microwave digestion procedure designed to give total element recoveries from many environmental samples. There is potentially quite a difference between leachable element content and total element content, and the magnitude of the difference could be unique to each different fertilizer sample matrix. Again, this has not systematically been investigated. There typically is a caveat in these E P A methods that says that other elements and matrices may be analyzed by the method i f performance is demonstrated for the analyte of interest, in the matrices of interest, and at the concentration levels of interest. For fertilizers this has not systematically been done, so the effectiveness of the E P A methods for fertilizers is not known. Besides variation in how samples are solublized, instrumentation commonly used for the determination step also varies. Frequently used instrumentation includes flame atomic absorption, graphite furnace atomic absorption, hydride atomic absorption, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. Each class of instrumentation is subject to its own limitations, and different analysts approach these limitations with varing levels of expertise. Much remains to be done in correlating data from different instrumentation.



64 Given the variation in methodologies available for metals analysis, it would not be surprising i f the current state of analytical agreement between laboratories doing this kind of analysis was not good. There is potential that, with 24 different state laboratories, not to mention fertilizer industry laboratories and commercial laboratories, all generating analytical data with this mix of methodologies, there could be considerable conflicting information generated. Here we report on a study designed to obtain an estimate of the degree of accuracy and precision possible by laboratories that may be asked to routinely monitor the trace metal content of fertilizer materials.

Survey Design The survey design was limited to only 5 samples and 5 elements: A s , Cd, Pb, Hg, and Se. Three of the samples were certified stock standard solutions of the 5 elements, diluted in 5% H N 0 . Solution one contained relatively low levels, representative of levels in average fertilizers. Solution two contained higher concentrations, but still below the allowed levels set by the A A P F C O SUIP25 document. Solution three contained levels above those allowed by the SUIP25 document. Analysis of these three solutions provided information on how well the laboratories were operating their various instruments, independent of digestion chemistry variation and sample matrix interference. The participating laboratories were free to use whatever instrumentation they chose. 3

Solution four was a real fertilizer sample, the Magruder check sample (http:// www.magruderchecksample.org/) for March of 2001, predigested in nitric acid by microwave (0.25g sample, 20mL H N 0 , digested 70sec). Analysis results for this sample included variance from matrix interferences as well as instrument variance. The fifth sample was an undigested solid fertilizer (the same Magruder check sample). The labs were instructed to digest this sample however they wished, according to their normal routine procedures. The variance associated with this sample would include instrument, sample matrix, and digestion. 3

A total of 29 laboratories participated in this study: 20 regulatory labs, 6 industry labs, and 3 others. The laboratories routinely analyze samples for trace element content, and would be expected to be many of the same state and industry laboratories conducting these analyses relative to regulatory activity.


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Results


Table I summarizes the digestion procedures, and Table II summarizes the instrumentation used, by the 29 laboratories. Note that just because two laboratories used the same digestion equipment (microwave or hot plate) and the same digestion acid combination, this does not necessarily mean that an identical digestion procedure was employed. Table I. Summary of Digestion Techniques Used by Laboratories Lab 1 2 3 4 5

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 24 25 26 27 28 29

As Digestion

Cd Digestion

Pb Digestion

MW HNO3 HP HNO3/HCI HP HNO3/HCI HP H N O 3

MW HNO3 HP HNO3/HCI HP HNO3/HCI HP HNO3 HP HNO3/HCI

MW H N O 3 HP HNO3/HCI HP HNO3/HCI HP H N O 3 HP HNO3/HCI

HP HNO3/HCI HP HNO3 MW HNO3 MW HNO3/HCI HP HNO3

HP HNO3/HCI HP HNO3 MW HNO3 MW HNO3/HCI HP HNO3 HP HNO3/H2O2/HCI HP HNO3/HCI HP HNO3/HCI HP HNO3/HCIO4/HCI

HP HC1

HP Dry AshHNC>3/HCl HP HNO3/HCI HP HNO3/HCI HP HNO3/HCIO4/HCI

HP HC1 MW HNO3/HCI

HP HC1 HP HNO3/HCI MW HNO3 HP HNO3/HCIO4

MW HNO3/HCI HP HNO3/HCI HP HNO3 HP HNO3/HCI MW HNO3 HP HNO3/H2O2

HP HN03/H 02\HC1 2

HP HNO3

HP HNO3

HP HC1 HP HNO3/HCI HP HNO3/HCIO4 HP HNO3/H2O2/HCI

HP HC1 HP HNO3/H2O2/HCI MW HNO3 HP HNO3/H2O2/HCI

HP HNO3/HCI HP H N O 3 MW H N O 3 MW HNO3/HCI HP HNO3 HP HNO3/H2O2/HCI HP HNO3/HCI HP HNO3/HGI HP HNO3/HCIO4/HCI MW HNO3/HCI HP HNO3/HCI HP HNO3 HP HNO3/HCI

MW HNO3 HP HNO3/H2O2 HP HNO3/H2O2/HCI HP H N O 3

HP HC1

HP HNO3/H2O2/HCI MW H N O 3 HP HNO3/H2O2/HCI

(MW is Microwave, HP is Hot Plate) Continued on next page.


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Table I. Continued Se Digestion

1 2

MW HNO3 HP HNO3/HCI

MW HNO3

HP HNO3 HP HNO3 MW HNO3/HCI HP HNO3 HP H N 0 / D r y Ash/HCl HP HNO3/HCI

HP H N O 3

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Hg Digestion

Lab

8 10 11 12 13 14 15 17 18 19 20 21 22 25 26 27 28 29

HP HNO3/HCI

MW HNO3/HCI HP H N O 3

3

HP HNO3/HCI

HP HNO3/HCIO4/HCI MW HNO3/HCI

HP HNO3/HCIO4/HCI HP HNO3 HP HNO3/HCI MW HNO3 HP HNO3/HCIO4 HP HNO3

HP HNO3/H2O2/HCI HP HNO3/HCIO4 HP HNO3/H2O2/HCI

HP HNO3/HCI MW HNO3/HCI HPHNO3/H2SO4 HP H N O 3

MW H N O 3

HP HNO3/H2O2 HP H N O 3 HP HC1 HP HNO3/H2O2/HCI

(MW is Microwave, HP is Hot Plate)


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Table II. Summary of Instrument Techniques Used by Laboratories Lab 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

As ICP-MS ICP-OES ICP-OES ICP-MS

ICP-MS GFAA AA Hydride AA Hydride A A Hydride GFAA

Cd ICP-MS ICP-OES ICP-OES ICP-MS Flame A A ICP-OES ICP-OES ICP-OES ICP-MS ICP-OES ICP-MS Flame A A ICP-OES ICP-OES ICP-OES Flame A A Flame A A Flame A A ICP-OES Flame A A ICP-OES GFAA GFAA Flame A A GFAA

Flame A A Flame A A ICP-OES ZGFAA ICP-OES GFAA GFAA Flame A A GFAA

ICP-OES ICP-MS A A Hydride ICP-MS

ICP-OES ICP-MS Flame A A ICP-MS

ICP-OES ICP-MS ZGFAA ICP-MS

ICP-OES ICP-OES ICP-MS ICP-OES ICP-MS AA Hydride ICP-OES ICP-OES ICP-OES AA Hydride A A Hydride

Pb ICP-MS ICP-OES ICP-OES ICP-MS GFAA ICP-OES ICP-OES ICP-MS ICP-OES ICP-MS Flame A A ICP-OES ICP-OES ICP-OES

Se ICP-MS ICP-OES ICP-OES ICP-MS

Hg ICP-MS

ICP-MS

ICP-OES ICP-OES ICP-MS AA Hydride ICP-OES ICP-OES ICP-OES A A Hydride AA Hydride ICP-OES ZGFAA ICP-OES A A Hydride AA Hydride AA Hydride AOAC Flourometric ICP-MS A A Hydride ICP-MS

ICP-OES ICP-MS

ICP-OES

Cold Vapor Cold Vapor ICP-OES Cold Vapor Cold Vapor Cold Vapor Cold Vapor ICP-OES ICP-MS



68 A statistical summary for cadmium, lead, and arsenic is given in Table III. For Cd, the three solutions prepared from accurate dilution of certified reference standards, Low, Intermediate, and High Stock Solutions, the mean of reported concentrations closely matched the True Value. In addition, the coefficients of variation (CV) for all three solutions were

Regulation of Heavy Metals in Fertilizer: The Current State of

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