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A tree ring record of environmental contamination - Emissions from the Palmerton, PA, USA, New Jersey zinc smelter

Eby, G. N.

Zinc mining first began in the Franklin, New Jersey, area in the 1700’s. In the late 1800’s the individual claims were consolidated into a single entity known as the New Jersey Zinc Company. The two mining operations were at Sterling Hill and Franklin Furnace. The major ore minerals were franklinite [(Zn,Mn²⁺,Fe²⁺)(Fe³⁺,Mn³⁺)₂O₄], willemite [Zn₂SiO₄], and zincite [(Zn,Mn²⁺)O]. These two mines are well-known to mineral collectors the world over as more than 300 different mineral species, including ~90 fluorescent minerals, have been identified at the two mines. In 1898 New Jersey Zinc built a smelter (West plant) at what became Palmerton, PA (named after Palmer, the president of New Jersey Zinc) and in 1911 a second smelter (East plant) was built. Smelting operations continued at these two plants until 1980. Ores from both mines were processed in Palmerton, but after 1954 (when the Franklin Furnace mine closed) only ores from Sterling Hill were processed in Palmerton. When operating, it was estimated that the smelters emitted 47 tons/yr of Cd, 95 tons/yr Pb, and 3,575 tons/yr Zn plus significant amounts of sulfur dioxide. The site of the abandoned smelters is now an EPA (Environmental Protection Agency) superfund site.

A tree ring core was extracted from an oak tree approximately 2 km downwind from the zinc smelters. The core encompasses approximately 150 years of history starting in 1860. Ten segments of this core (ranging in mass from 167 to 351 mg) were analyzed for 25 elements using Instrumental Neutron Activation Analysis (INAA). This is the method of choice in this case because (1) it obviates the problem of obtaining a complete solution which is required by solution methods, (2) its high sensitivity for a number of the elements of interest, and (3) it is nondestructive (the same samples were subsequently used for a stable isotope study).

Metals can be delivered to the tree either by deposition on the leaves or by cycling of the metals through the soil-root system. The metals are subsequently incorporated into the tree and are lodged in the ring wood. The data from the tree ring sequence reveal the following (1) by 2005 for most metals the concentration had returned to pre-smelter values, (2) Au and Co increased throughout the period of smelter operation, (3) Se, Sb, As, Sc, and U values increased from the time that smelter operations started until around 1950 when their concentrations began to decline, perhaps a response to the suspension of smelting of the Franklin Furnace ores, (4) Na and Zn concentrations remained relatively constant, and (5) K concentration declined throughout the period of smelter operation, which may reflect the loss of K due to acid deposition. Thus, the tree rings record the history of smelter operations and reflect the impact of the contaminants on the tree.

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Instrumental neutron activation analysis (INAA) and its application to forensic investigations

Eby, G. N.

Instrumental Neutron Activation Analysis (INAA) is a straightforward technique for determining elemental abundances in a wide range of materials. The interaction between a thermal neutron and a nucleus produces a radioactive nuclide that emits characteristic gamma rays. The energy of the emitted gamma rays is used to identify the nuclide and the intensity of the radiation can be used to determine abundance. Solid state detectors are used to sense the emitted gamma rays. Following decay and interference corrections, elemental concentrations are determined. The advantages of INAA are (1) it is a relatively cheap analytical method; (2) the method is non-destructive and the same sample can be used for other measurements; (3) sample size can be very small, often as little as a milligram; (4) detection limits for many elements are in the nanogram range; (5) no chemical preparation is required; and (6) on the order of 40 elements can be measured essentially simultaneously.

There are numerous potential applications of INAA in forensic investigations. The underlying concept is that materials within a class will have different elemental signatures. For example: (1) The elemental composition of maple syrup is determined by the chemical composition of the sap which reflects the underlying soil chemistry, elements introduced during the tapping of the tree and transport to the sugar house, and elements introduced during the boiling down of the sap to produce maple syrup. Maple syrup from different sources can be chemically fingerprinted. (2) Grass chemistry varies as a function of soil chemistry which in turn is related to the chemistry of the underlying bedrock. These variations can be used to identify the geographic location of a grass sample. Similarly mineral exploration geologists have used chemical variations in plants to identify potential ore deposits and geochemists have looked at the relationship between plant chemistry, soil chemistry, and human health. (3) Ceramics consist of mineral components and transition metals that are added for color. For example, Zircopax (essentially zircon) may be added to glazes and this addition leads to a distinctive enrichment in HREE. Co is added for color. Different combinations of minerals and elements in a glaze produce characteristic elemental signatures.

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Forensic geology as a vehicle for inquiry-driven learning - the case of the sandy body

Eby, G. N.

Forensic Geology can be used as a vehicle to introduce students to geological concepts and principles using an inquiry driven approach - i.e., crime solving. We have developed such a course largely based on case studies. The course was designed for non-science majors, but biology, chemistry, and physics majors have taken the course as a technical elective. The Case of the Sandy Body is an example of the approach we use in this course.

The case starts with a body dumped in a classroom. The body is wrapped in cloth and there is abundant sand. Students first exam the crime scene and collect evidence using standard forensic techniques. The students are then provided with a narrative concerning the whereabouts of the victim in the past 24 hours and samples of sand from locations where the victim was sighted.

The students do a size analysis of the sand associated with the victim and the various possible crime scene locations. They microscopically examine the various sand samples and characterize them in terms of texture and mineralogy. In order to do this students must know something about mineral identification and at this point a standard mineral identification laboratory is done. The students also prepare heavy mineral suites using a magnetic separator and identify the minerals in each heavy mineral suite. All the information is collated and a comparison is done between the sand collected from the victim and the comparative samples. From this comparison students identify a potential crime scene.

Students are then provided with photographic evidence from the potential crime scene including a sneaker imprint. The case continues with a routine traffic stop in the area of the crime scene leading to the apprehension of a suspect who has sandy sneakers in the back of his car (its a station wagon and the sneakers are in plain view). The students are given the sneakers and asked to compare the sand adhered to the sneakers and that from the victim. Most times, but not always, a match is found. The final step is the preparation of a forensic report using standard reporting procedures.

Our experience is that the students become very engaged in solving the crime. They learn material typically covered in an introductory geology course but in a problem-solving context. Student response to the course has been very positive.

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Forensic Geology Lectures:

Minerals - Definition, Types, and Identification - Forensic Applications

Instrumental Neutron Activation Analysis (INAA) and X-ray Fluorescence (XRF) Analysis – Practice and Applications

Radioactive and Stable Isotopes - Theory and Application to Forensic Investigations

Other Geological Applications to Forensic Investigations – Rocks, Geologic Maps, and Building Materials

Oklahoma Forensic Geology talk

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Press Releases:

Nature Blog - Geological Society of London Forensic Geology Meeting 2008

Bogota, Colombia INAA 2009