Toxic backlinks are links that are not from high-quality or trusted authority sites. In the long run, they can definitely hurt your SEO so it is important to know how to identify them and understand what to do if you find you have them.
You can identify the links first by using the Google Webmaster Tool and checking the anchor text of the link. As Google expert Dr. Marie Haynes said, “A lot of links that have been acquired by unnatural means will often be keyword anchored”.
If the link looks or sounds suspicious, and doesn't coincide with your niche, it can be a strong indication that it's a spam link.
To remove them, you will need to use Google Search Console to disavow them. As a bonus, Neil has written a detailed guide on how to do that here.
It is also important to know that when you disavow spammy links, it could take time. Experts say, it can take up to 9 months but there isn't really any surefire way to know if the disavowed links are actually ignored or not, unfortunately.
Generally speaking, spammy links can only be removed whenever Google recrawl those links and decide whether to ignore them or not. In worst-case scenarios, it's still possible for the disavowed links to appear in your Google Search Console and never be removed.
Please feel free to reach out to us if you have any questions, suggestions, or complications at firstname.lastname@example.org.