There is not much to google about the cement plants because there aren't any issues, as far as I am aware. I believe the EPA does testing on air quality and it's ok everywhere. Living here, no one talks about it and I haven't noticed anything.
Schools: i believe all the MISD schools are good and there isn't a preferred area. You could go to the accountability ratings website for performance, demographics, and general data overload to compare them. I remember researching and liking the long branch elem / walnut grove middle route. I can vouch that long branch elementary is a great elementary school and I have high hopes for midlothian heritage high school, both in terms of having strong academics and being small enough that my kids could participate in sports, maybe even -gasp- more than one sport.