Secondhand smoke and behavior problems

Yeah, I know, another one on smoking. They've linked the MOTHER's smoking to behavior problems in kids, but this one says the link is there with kids exposed to secondhand smoke as well:
Children of smokers, as well as of women exposed to secondhand smoke, were much more likely than the offspring of non-exposed women to have externalizing behaviors, which include "acting out, getting in trouble, being aggressive, breaking rules," Gatzke-Kopp noted.
Scientists believe such behaviors are controlled by the brain's dopamine system, which has been shown in animal studies to be damaged by fetal smoke exposure.
"Evidence suggests that the dopamine system in the brain gets over stimulated during pregnancy," Beauchaine noted in a statement. "As a consequence, children who were exposed to smoke in utero have colic and are hard to soothe as infants. As toddlers they are overactive and oppositional. Later on they are irritable, inattentive and low on pleasure."

I find that interesting because my kids have been accused of being hyperactice and they are hard to discipline (meaning to teach to behave). Leanna and Timothy in particular are oppositional! Justin was/is colicky, which I believe is partly just his personality but maybe exaggerated by the secondhand smoke? (Or the lead exposure? wherever it comes from?). I really think a number of factors combine to make my kids on the difficult side. I don't mean that it's all bad, they are naturally very curious and very creative and those things sometimes combine with the negative traits, making trouble. I get very frustrated by this though, because I think it often looks as though my children aren't diciplined, WHICH IS NOT THE CASE! My Mom recently commented that she thinks I'm getting better at discipline. I'm not really doing things differently. Maybe it's because she's around more since she's not working so she sees more of it? Maybe it's because she HEARS me yelling more (though that's not a good thing, in my opinion) because I lose my patience quicker than before. I used to be the most patient and calm person. Really!! Now I'm alone long long hours with just me and the kids and I get worn down so much easier. I've also picked up my husband's bad habbit of yelling loudly. I hate when he does it but I find I've unfortunately picked it up myself. It really does nothing but teach the kids to yell loudly when they get mad also. And I think in the long run it makes you less effective. It's something we have to work on.
Anyway, my point is that a study like this makes me wonder if the secondhand smoke isn't a contributing factor in their behavior. Not the only factor, just one of several. I certainly acknowledge that I am not perfect and often don't react as I should. I'm a work in progress too. Either way, it's interesting to note that even if the mother isn't smoking herself the secondhand smoke can still cause problems, mental and physical, for the children.