Anthropogenic Coal Ash as a Contaminant in a Micro-meteoritic Underwater Search

Patricio A. Gallardo

Published October 2023 • © 2023. The Author(s). Published by the American Astronomical Society. 

 

Abstract

Chemical composition for spherules recovered from the search area of CNEOS 2014-01-08 in the Pacific Ocean has been recently released. A three-order of magnitude difference from CI-chondrites has been identified for elements beryllium, lanthanum and uranium in five samples. The lack of consensus regarding atmospheric survival and precision of path estimates motivate an examination of possible contaminants. Contents of nickel, beryllium, lanthanum and uranium are examined in the context of a known anthropogenic source of contamination, and found to be consistent with coal ash as suggested from a publicly available coal chemical composition database (COALQUAL). The meteoritic origin is disfavored.

1. Introduction

An expedition to locate micrometeoritic fragments in the search area of CNEOS 2014-01-08 has been announced and conducted in the South Pacific Ocean (Loeb 2022 and Loeb et al. 2023, L23 hereafter). A magnetic sled was used to retrieve magnetic material. Round objects in the ranges from hundreds of microns to millimeter scales have been reported. It has been suggested that the high concentration of beryllium, lanthanum and uranium in five samples (named BeLaU for short) could be anomalous as compared to CI-chondrite abundances (L23). However, few comparisons to contaminants have been conducted to discard the null hypothesis of terrestrial contamination. The lack of consensus regarding the atmospheric survival and precision in the determination of the path of CNEOS 2014-01-08 (Vaubaillon 2022; Brown & Borovička 2023) motivate a discussion of possible sources of contamination from terrestrial sources.

Multiple reports during the past century have discussed anthropogenic contaminants in samples containing magnetic spherules from microns to millimeter scales in size (Handy & Davidson 1953; Oldfield et al. 1978; Goldberg et al. 1981; Deuser et al. 1983; Locke & Bertine 1986; Wik & Renberg 1991). Most notably, in 1976, another naval expedition in the Gulf of Mexico found large numbers of magnetic spherules from anthropogenic sources in seawater (Doyle et al. 1976). Chemical composition analyses revealed consistency with coal fly ash, a waste product of the combustion of coal in power plants and steam engines.

In this document, the chemical composition of the five spherules labeled BeLaU in L23 is analyzed in light of a known source of contamination from anthropogenic origin such as coal fly ash. Iron content is compared to previously published data from a naval expedition, which collected magnetic spherules as presented in Doyle et al. (1976) and to the iron contents in fly ash retrieved from a real power plant as in Hock & Lichtman (1983). The contents of beryllium, lanthanum, uranium and nickel are compared to expected abundances using publicly available measurements from coal quality data maintained by the USGS as in Palmer et al. (2015). This document is organized as follows: Section 1 gives a brief summary of the expedition, findings, and a description of this work. Section 2 discusses the methods used to compare abundances. Section 3 describes the results. Section 4 concludes.

 

2. Method

2.1. Iron Composition

The iron content of coal ash has been documented in the context of coal quality control and commercial iron sourcing. Although typical values for the iron content in coal ash range 20%, with a variance of several tens of percent (Myers et al. 1973), higher values can be obtained if the ash is magnetically selected (Murtha & Burnet 1978). Spherule size is another source of bias as discussed in Czech (2022). Iron content in a real power plant was presented in Hock & Lichtman (1983), where samples were collected at the plant smokestack, reporting 35% iron concentration with a standard deviation of 30%.

In one report from a naval expedition (Doyle et al. 1976), seawater was microfiltered and the resulting spherules were magnetically identified. In this experiment, spherules were identified as athropogenic fly ash via their composition. Due to the similarity of the experiment presented in Doyle et al. (1976) and in Loeb (2022), the iron content reported in Doyle et al. (1976) is used to compare the range of iron abundances, considering that a variation of several tens of percent is expected from practical ash.

2.2. Beryllium, Lanthanum, Uranium and Nickel Content

Publicly available coal quality data COALQUAL summarized in Palmer et al. (2015) is used to obtain the range for the concentrations of five elements: nickel, beryllium, lanthanum and uranium in coal ash. Coal quality databases report trace abundances according to the formula

where

is the concentration of element X in an ash-basis or coal-basis, and f is the ash fraction, the amount of matter that survives burning.

3. Results

3.1. Iron

The abundance reported in Table 1 in Doyle et al. (1976) has a mean value of 68%, while the iron abundance in the BeLaU sample has a mean of 51%. In consistency with Hock & Lichtman (1983).

3.2. Nickel

Nickel content has been pointed out as a discriminator between coal ash and meteoritic material (Handy & Davidson 1953). Table 1 in Doyle et al. (1976) found nickel concentrations of order 0.04% in fly ash. The nickel concentrations in L23 are of order 200 ppm (0.02%) or lower. Which puts the nickel content in the same order of magnitude of Doyle et al. (1976).

In addition, COALQUAL data as described in Section 2 is used as a comparison. Figure 1 (bottom right) shows in green the concentrations of the five BeLaU samples, the histogram shows the expected nickel concentration from the COALQUAL database. Nickel content is in consistency with ash from coal.

Figure 1. Beryllium, lanthanum, uranium and nickel concentrations in BeLaU (green) samples. Histogram shows frequencies obtained from COALQUAL. Concentrations are within expectation for all elements.

 

3.3. Beryllium, Lanthanum and Uranium

Figure 1 shows in green the concentrations for the five BeLaU samples, with the expected histogram (in black) of the concentrations from coal ash for beryllium, lanthanum and uranium. COALQUAL data shows that all samples are in the expected range, in consistency with coal ash, and with: Headlee & Hunter (1953), and Zielinski & Finkelman (1997).

4. Conclusion

A compositional comparison of five samples collected from the Pacific Ocean has been presented. The content of iron and nickel have been compared to a previous report of an ocean expedition, which collected water samples using microfilters and collected spherical magnetic objects. The contents of beryllium, lanthanum, and uranium were compared to a publicly available database of coal composition.

Iron content is found to be consistent from previous reports of coal ash contamination. Nickel, beryllium, lanthanum, and uranium concentrations are found to be consistent with expectations from coal ash from a coal chemical composition database. Fly ash resolves the three-order of magnitude difference from comparisons to CI-chondrites. The meteoritic origin is disfavored.