A dangerous amount of arsenic would seem be a dangerous living condition and a violation of the implied warranty of habitability. The failure of 1st floor windows to lock could be dangerous, if you live in an area where they are signficant security concerns. Violations of the implied warranty would give rise to the right to sue for monetary compensation--such as rent abatement, or a retroative pro rate rent reduction--for the period of time you lived with such conditions. You could also potentially sue for any medical costs (such as if you should be tesed on account of the arsenic.) You could potentially threaten to, or at need, actually, sue if the landlord improperly keeps your security deposit. Bearing in mind that no lawsuit is every guaranteed, you do seem to at least have a colorable claim which you could interpose.Also, even if you actually did the damage described (screen door, gate), the landlord could only retain such portion of the deposit as is necessary to actually pay for repairs--for example, say that your deposit was $1,000, and it would take only $400 to fix the problems; in that case, the landlord could only take $400 from the deposit. If the landlord withholds too much from your deposit, you could sue for the return of the balance, either as a separate suit or as part of an action based on a violation of the implied warranty of habitability.