Conducting a Literature Review
Table of Contents
- Introduction to Literature Reviews
- Steps of an environmental monitoring literature Review
Introduction to Literature Reviews
When preparing for a tool development project or an environmental study, conducting a literature review is one of your very first steps. A literature review is the process of reading a broad array of published information, most often in journals or official reports, that provide a contextual framework and supporting evidence for your anticipated work. In journal articles, the “background” or “introduction” sections are typically concise and tailored summaries of the author’s literature review for that piece. The purpose of a literature review is to build your knowledge, provide context to situate and evidence to support your work, and thereby increase your likelihood for success. Information gleaned from a literature review generally includes topics and techniques that have been explored in this area, the currently known best practices, and relevant ancillary or associated subject areas or data. Literature reviews can also lead you to identify relevant gaps in knowledge or data, which can be important to highlight in order to stimulate research in that area or underlie the importance of your work if it applies to filling that gap.
A literature review is an important piece of every project, and you often need to do several rounds of literature reviews as your project progresses. A literature review is necessary before starting any technological development, scientific, monitoring, or advocacy project. The foci of literature for these different types of projects will be different, but all will be in an effort to provide context and guidance for your project.
The first step in conducting a literature review is to clarify what the purpose of your literature review is. For example, are you interested in building a low-cost conductivity meter and need to conduct a literature review to learn how others have measured conductivity, what potential interferences there may be, how conductivity is quantified and verified, etc? Or, are you experiencing shortness of breath and want to learn about whether or not certain chemical exposures may result in such health symptoms, and what steps you can take to mitigate exposure? Or, do you think the landfill nearby may be negatively impacting air quality and you want to learn what kinds of pollutants are generally associated with landfills and what relevant regulations exist? If you are not entirely sure yet of your purpose for a literature review, the best general approach is to start broad and successively narrow and deepen your scope.
Steps of a Literature Review
For a literature review at the start of a low-cost environmental monitor development process, the principal steps are:
1. Search for basic information about the parameter of interest
You’ll want to learn information about what this substance or signal is, where it is commonly found, and what the sources of it to the environment are. You may also be interested in learning what effects of this substance are (e.g. human or ecological health impacts). This purpose of this step is to provide very broad context. Good sources of information include textbooks, educational websites (including government websites), “introduction” sections of publicly available masters theses and doctoral dissertations, and “introduction” sections of open-access journals. People who are well-versed in the topic also are an excellent resource; research librarians at public libraries or public university libraries may be able to point you to useful literature and help build your vocabulary for the topic. In this first part of the literature review, trusted websites can be a good place to start, such as university extension service websites, public health department websites, environmental protection department websites, etc. For textbooks, many teachers and professors post their syllabi online, and you can search for the topic or subject area followed by “syllabus.” A general Google search including the word “dissertation” can be useful for finding dissertations, or you could try this website dedicated to promoting and preserving dissertations: http://www.ndltd.org. To find open access journals, the Directory of Open Access Journals (https://doaj.org/) is a great place to start. At this point in the process, reading primarily introduction sections will help you build broad context.
2. Search for sample collection and analysis methods
Once you have a contextual understanding of the topic at hand, it is then necessary to find out how people typically measure the substance. To do this, key places to look include government official methods (e.g. published by EPA, NIOSH, etc) and academic papers’ “methods” sections. You can also call a commercial laboratory who tests for the contaminants of interest, or university professors who research the topic and ask for the methods they use. These methods sections will likely have a lot of technical language and require time to discern. For each instrument described in the method, take time to learn, usually through additional searches and websites, what that instrument is and how it operates. To find journal articles where you have access to the full text so you can read the methods section, you can try searching at a local university library or again look to open access journals. In addition to fully open access journal articles, articles that aren’t technically open access are often available online too. To find journal articles, there are a few free online search engines like Google Scholar. Generally the links included in a Google Scholar search will take you to a journal website where you can at least read the abstract, and sometimes the full article. As you try using different search terms in the search engine, keep a record of which terms yield more useful results, and start to build your vocabulary for this field. Also, note if there is a journal that comes up often in the search results, as it may be a popular journal for that topic and could be a good place to start an in-depth dive. If only the abstract from the search engine result is available on the journal website, try typing the full title into a basic Google search to see if any full text versions are linked. If none of the top ten results for a journal article is linked to the full text, you can try searching on the authors’ websites, where they may have posted their articles. If you live near a university, you may be able to use computers in their library to search their electronic databases for full text articles as well, but check with the librarian first. Read the methods section of the full text articles, and note the papers that are cited in that section. Read each of the cited papers, as those are typically the papers with the fundamental findings for new instrumentation and methods. Full papers discussing method development can be very useful, as they will often include sections describing common interferences, which are important to remember when assessing the suitability of a method for your purposes. As you read these papers, keep in mind the potential for this method to be conducted outside of laboratory settings, considering questions like whether or not the reactants are safe, what sorts of energy requirements are necessary, and whether or not lower-cost materials could replace specialized equipment.
3. Search for historical measurement methods
After learning about how the parameter is typically measured in labs today, especially if those common methods are not suitable to use outside of the laboratory, learn about how this substance has been measured in decades past. Search engines like Google Scholar can be useful for this, narrowing your search by date, going progressively further back in time. Another way to approach this is to look at the oldest papers cited in papers you have read on this topic, and read that oldest citation’s methods section. If that paper does not have a methods section, search in a search engine constraining the dates to ~5 years around when that oldest citation was published since there was likely more research being conducted on the topic around that same time. Continue looking for older citations, especially citations in the methods section, to find foundational technologies and techniques. It can also be advantageous to speak with someone who is a veteran in the field to learn historic methods for measuring a substance. Try contacting the author of a publication who has either been in the field for many years or published in the field many years ago. You can also search for old patents related to measuring this substance, but many patents do not provide as useful of information as established methods do. It may be useful to learn whether or not patents do exist for technologies of interest though. Searching patents.google.com is good place to search for patents, and you can also search the US patent office: http://www.uspto.gov/patents-application-process/search-patents. Remember that most patents have a term of 20 years, so older technologies may be more accessible.
4. Search for relevant regulations
Once you have learned about how the parameter of interest can be measured, it is important to learn how it is regulated. Many regulations are technology-based, meaning that their data is only accepted by enforcement agencies if specific instruments were used and specific methods were followed. If your goal is to persuade environmental enforcement agencies that your data indicates the need for enforcement or other action by an authority, it is crucial that you understand the requirements for data to be used in an official capacity by that agency. To do this, first search the state environmental department or health department for the substance to find out their methods. If the method does not appear on the department website, you can search the relevant state administrative code pertaining to environmental regulations, and methods will often be cited there. From the methods cited in the administrative code, you will most likely need to search for those methods on the EPA website, and dive deeper into methods on the EPA’s technology transfer network, https://www3.epa.gov/ttn/.
Learning about the criteria that constitute a violation for this substance is crucial to study and technology design goals. To learn about the state regulations, read state administrative code for the environmental department. This can be a long and tedious process, but can provide extremely useful information. For state codes that simply reference federal codes, you can try to read the corresponding federal register (https://www.federalregister.gov/), however, several errors have been found on the electronic site (e.g. claiming to be current federal code, but presenting statutes in 2016 that became out-of-date in 2012). Searching the EPA technology transfer network and related websites contain the necessary information, and tend to be more user-friendly. Once you have read and catalogued the relevant regulatory information, think through data collection requirements (e.g. sample collection length and intervals, etc).
It may also be worthwhile to look at related regulations in the state administrative code, such as other regulations pertaining to smokestack emissions even if the primary substance of interest for you is sulfur dioxide. This may help you navigate alternative study designs if measuring the substance of interest isn’t feasible.
5. Look for proxies or indicator species
If the contaminant of concern is very difficult or expensive to measure, a more feasible approach may be to monitor another substance that has a demonstrable relationship with the contaminant of concern, which can be considered a “proxy” or “indicator” for the substance of interest. For example, if you are concerned about specific biocide chemicals in hydraulic fracturing waste spilling from trucks into a stream, it may be less costly to monitor another compound found in high concentration in hydraulic fracturing waste. In this example, since hydraulic fracturing waste is extremely briney, it may be worthwhile to monitor the stream for spikes in conductivity, which would occur if hydraulic fracturing waste were spilled.
Figuring out what is an appropriate proxy or indicator species for the actual contaminant of concern can be extremely challenging. There should be evidence that the proxy and the contaminant of concern co-occur and that there is not another likely source of the proxy substance that would impact the study. For instance, in the example above, conductivity spikes would not be an appropriate indicator of potential hydraulic fracturing waste spillage if it were winter in an area that salts roadways because roadway salt runoff could also cause a spike in conductivity. It is important to note that there are always limitations to using proxies because there are rarely exact relationships, but as long as there is a feasible relationship that can be clearly articulated, it can be worthwhile.
To find likely proxies, the best place to start is to learn more about the potential source of the contaminant. Does that source also act as the source for another kind of contamination? For example, if you are concerned about exposure to airborne diesel combustion products but don’t have the means to measure them, could you start by counting heavy truck traffic and build a case from there? If you are concerned about illegal discharge from a plastics manufacturing facility but do not have chemical-specific analytical capabilities, could you monitor for a temperature increase in the water that would occur from an industrial discharge?
In addition to looking for proxies that come from the same source as your contaminant of interest, you can also look for effects of that contaminant. For example, if you are concerned about elevated nutrient concentrations coming from agricultural runoff but don’t have nitrate or phosphate sensors, could you monitor algae growth that would be stimulated by the nutrient excess? If you are concerned about the pH of a stream but don’t have equipment to monitor for that, could you count different species of macroinvertebrates to observe the presence or absence of pH-sensitive species?
It is important to note that proxies and indicators cannot tell you explicitly if your contaminant of concern is present or at what level, but could potentially lend enough evidence to warrant further investigation.
6. Conduct a health effects literature review
If you are conducting an environmental monitoring study due to concern about people’s health, it is necessary to do a thorough literature review about health effects and/or toxicology of your contaminant of concern. We have written a specific guide to conducting this sort of literature review, found here. Conducting literature reviews to provide information about health effects and risk factors can be particularly challenging, due to the variation in human response and the difficulty in isolating cause and effect in human health studies. Ultimately you likely want to discern what exposure levels have negative health impacts, what those health impacts are, and if there are any particularly vulnerable populations. Exposure levels will vary by contaminant concentration, exposure duration, and exposure frequency. Health effects can be impacted by exposure level and a person’s (or population’s) vulnerability, and often by compounding factors such as other contaminants co-occurring or which chemical species of the contaminant is present. Facets of information you want to be aware of when looking through health studies include: who the study population was, what type of exposure it was, what species of the contaminant was studied, and where or how that type of exposure is likely to occur.
Places to start your literature review for health effects include the Center for Disease Control (CDC) and the Agency for Toxic Substances and Disease Registry (ATSDR). These websites have compilations of information about a variety of contaminants with negative health impacts. Unfortunately, the information synthesized on the ATSDR website doesn’t include primary literature citations, but their compilation of information is quite valuable as an introduction to the subject. The contaminant’s “Toxicology Profile” published by ATSDR is an excellent resource, as it describes specific studies in detail. The CDC website has a very useful repository of primary literature and direct link to the ATSDR contaminant Toxicology Profile, listed on the “Publications” page that can be navigated to from the CDC’s homepage of your contaminant of concern. The Toxicology Profile and the various case studies included in the publications page can be essential to your literature review as they will provide the information you seek with regards to exposure-related health impacts.