Getting started with ccdR:
Introduction Vignette

Center for Computational Toxicology and Exposure

Introduction to the CompTox Chemicals Dashboard (CCD)

Accessing chemical data is a vital step in many workflows related to chemical, biological, and environmental modeling. While there are many resources available from which one can pull data, the CompTox Chemicals Dashboard (CCD), built and maintained by the United States Environmental Protection Agency, is particularly well-designed and suitable for these purposes. Originally introduced in The CompTox Chemistry Dashboard: a community data resource for environmental chemistry, the CCD contains information on over 1.2 million chemicals as of May 2024 and has been cited 612 times according to CrossRef. To learn more about the CCD, please visit the page About CCD.

The CCD includes chemical information from many different domains, including physicochemical, environmental fate and transport, exposure, usage, in vivo toxicity, and in vitro bioassay data. For information on data sources and current versions, please review the CCD Release Notes. It provides a graphical user interface that allows for an interactive user experience and is easy to navigate. As such, users can explore the data available on the CCD without any programming background.

The CCD can be queried for one chemical at a time or using batch search.

Application Programming Interfaces (APIs) for Automated Batch Search of the CCD

Recently, the Center for Computational Toxicology and Exposure (CCTE) developed a set of Application Programming Interfaces (APIs) that allows programmatic access to the CCD, bypassing the manual steps of the web-based batch search workflow. APIs effectively automate the process of accessing and downloading the data that populates the CCD.

The CTX APIs are publicly available at no cost to the user. However, in order to use the CTX APIs, users must have a individual API key. The API key uniquely identifies the user to the CCD servers and verifies that you have permission to access the database. Getting an API key is free, but requires contacting the API support team at

The APIs are organized into sets of “endpoints” by data domains: Chemical, Hazard, and Bioactivity. An endpoint provides access to a specific set of information and data, e.g. physical-chemical properties for a chemical that the user specifies. A view from the Chemical API web interface is pictured below.

Figure 4: CTX API Chemical Endpoints
Figure 4: CTX API Chemical Endpoints

On the left side of each domain’s web interface page, there will be several different tabs listed depending on information requests available within the domain. In Figure 4, the Chemical Details Resource endpoint provides basic chemical information; the Chemical Property Resource endpoint provides more comprehensive physico-chemical property information; the Chemical Fate Resource endpoint provides chemical fate and transport information; and so on.


Authentication, found in upper left tab on each web interface page, is required to use the APIs. To authenticate themselves in the API web interface, the user must input their unique API key.

Figure 5: API Key Authentication
Figure 5: API Key Authentication

Request Construction

APIs effectively automate the process of accessing and downloading the data that populates the CCD. APIs do this via requests using the Hypertext Transfer Protocol (HTTP) that enables communication between clients (e.g. your computer) and servers (e.g. the CCD).

In the CTX API web interface, the colored boxes next to each endpoint indicate the type of the associated HTTP method. GET is used to request data from a specific web resource (e.g. a specific URL); POST is used to send data to a server to create or update a web resource. For the CTX APIs, POST requests are used to perform multiple (batch) searches in a single API call; GET requests are used for non-batch searches.

You do not need to understand the details of POST and GET requests in order to use the API. Let’s consider constructing an API request to Get data by dtxsid under the Chemical Details Resource.

Figure 6: Get Details by DTXSID
Figure 6: Get Details by DTXSID

The web interface has two subheadings:

  • Path Parameters contain user-specified parameters that are required in order to tell the API what URL (web address) to access. In this case, the required parameter is a string for the DTXSID identifying the chemical to be searched.
  • Query-String Parameters contain user-specific parameters (usually optional) that tell the API what specific type(s) of information to download from the specified URL. In this case, the optional parameter is a projection parameter, a string that can take one of five values (chemicaldetailall, chemicaldetailstandard, chemicalidentifier, chemicalstructure, ntatoolkit). Depending on the value of this string, the API can return different sets of information about the chemical. If the projection parameter is left blank, then a default set of chemical information is returned.

The default return format is displayed below and includes a variety of fields with data types represented.