How Many Chemicals in Commerce Have Been Analyzed in Environmental Media? A 50 Year Bibliometric Analysis

Over the past 50 years, there has been a tremendous expansion in the measurement of chemical contaminants in environmental media. But how many chemicals have actually been determined, and do they represent a significant fraction of substances in commerce or of chemicals of concern? To address these questions, we conducted a bibliometric survey to identify what individual chemicals have been determined in environmental media and their trends over the past 50 years. The CAplus database of CAS, a Division of the American Chemical Society, was searched for indexing roles “analytical study” and “pollutant” yielding a final list of 19,776 CAS Registry Numbers (CASRNs). That list was then used to link the CASRNs to biological studies, yielding a data set of 9.251 × 106 total counts of the CASRNs over a 55 year period. About 14,150 CASRNs were substances on various priority lists or their close analogs and transformation products. The top 100 most reported CASRNs accounted for 34% of the data set, confirming previous studies showing a significant bias toward repeated measurements of the same substances due to regulatory needs and the challenges of determining new, previously unmeasured, compounds. Substances listed in the industrial chemical inventories of Europe, China, and the United States accounted for only about 5% of measured substances. However, pharmaceuticals and current use pesticides were widely measured accounting for 50–60% of total CASRN counts for the period 2000–2015.

*Corresponding author : derek.muir@sympatico.gc.ca Summary : 15 pages, 6 Tables, 6 Figures   Table of Contents   Text  page 1. Further details on the CAS Search 2. Further discussion of Table 1 S3 Tables   Table S1. List of chemical lists/databases used to screen the BIOL/occur search S4 Table S2. A. Classes of substances removed from the ANST/POL list Table S2. B. Classes of substances in the ANST/POL list and illustrated in Figure 3 S7  Table S5. Comparison of reports for the top 5 pharmaceuticals in environmental samples S10

Further details on the CAS Search
We developed a targeted CAS Role search for substances associated in citations reported in analytical studies (ANST) and as a pollutant (POL). It can be referred to as a 'linked' CAS Role search. CAS roles are CAS indexing terms consisting of codes that describe the new or novel information reported about a substance or a class of compounds "POL" or "Pollutant": Defined by Chemical Abstracts (Vol. 66, 1967 to present): Assigned to a substance in studies in which the substance (viewed as a harmful substance) is encountered in the environment, including indoor and outdoor air and atmosphere, soil, water, buildings, biological systems, etc. This role is also used for substances in studies which focus on potentially harmful effects if the substance were to enter an ecosystem. In analysis for pollutants in environmental samples, the pollutant-analyte receives ANST and POL.
"ANST" or "Analytical Study". Defined by Chemical Abstracts (Vol. 66, 1967 to present): Assigned to a substance/material in studies of the detection or identification of the constituents of the material; of the determination of the amount of a constituent in the material; of qualitative or quantitative bioassays; of involvement of the substance in an analytical procedure; for separation of the substance with analytical intent; or for identification of an unknown substance. ANST roles are not assigned to the substance when a routine analytical procedure is used as a tool to verify results of a reaction or process.
"BIOL or Biological Study/RL. Defined by Chemical Abstracts (Vol. 66 1967 to present): Assigned to a substance in studies of the role of the substance in or its effect on biological molecules and systems (including organisms, organs, cells, and subcellular systems). Such studies include metabolism, toxicity, occurrence, biological applications and composition.
We used CAS STN (About CAS STNext® | STN International (stn-international.com) to search the CAS Content Collection. Unfortunately, this search approach cannot be performed/duplicated in CAS SciFinder, although the same database content is available on both platforms. However the search functionality is not equivalent. STN allows users to start at the CAS Role level for substances without searching for citation concepts. Our approach was to isolate substances with the appropriate linked roles first.
2. Further discussion of Table 1 "Total CASRN citation reports": Initially 105,410 citations were identified that contained the dual substance role indexing of ANALYTICAL STUDY and POLLUTANT. The Report citation count represents the number of citations where the identified CAS RNs are present. That resulted in an initial list of 23,458 unique CAS RNs associated with those roles in those citations. "Total CASRN citation counts" represents the total number of substance hits across those citations. A single citation may have 8 substances associated with those roles, leading to a count of 8 for CASRN Count. A substance would only be counted once in each citation, but a citation may have multiple qualifying substances.