I am doing my research on wetlands especially ecotoxicology aspect. Please suggest some peer reviewed journals which do not charge for processing and publication.
I'm new to the whole "publication world" too, but I can suggest the next webpage: https://www.journalguide.com/. It gives you options of journals based on key words or proposed publications titles.
Another suggestion is that you look at the names of the journals you cite the most, maybe they are where you can find your main audience.
In my own and limited experience, I'm familiar to "Wetlands", "Wetlands Ecology & Management", "Ocean and Coastal Management", "Estuarine, Coastal and Shelf Science", "Environmental Research" and "Journal of Coastal Research", but while interesting in mangrove ecology and restoration, I'm not into pesticide dynamics of effects.
If your study is of local interest or is descriptive, then send your article to your local botanical or ecological journal. If it is is of greater significance, or broader appeal, you can consider bigger international journals such as Ecology, Ecography, etc. Don't worry if you have to pay – it's more important to be in the journal you like even if you have to pay for it. You won't regret it :)
I can recommend you, of course, a Journal from Romania, where I am a member of the Editorial Board: Geo-Eco-Marina.
Geo-Eco-Marina is listed in SCOPUS, Directory of Open Access Journals (DOAJ), Zoological Record, EBSCO Central&Eastern European Academic Source, ProQuest - Scientific Journals Database, Google Scholar etc.
Wetlands is appear reviewed journal you may think of. Wetlands Ecology and Management could be another depending on where you want to publish your research works.