Can I hold my landlord responsible for mold issues and health problems after I informed him of a serious problem that he neglected to address?

The Virginia Residential Landlord and Tenant Act sets forth the rights and responsibilities of landlords and tenants. According to Section 55-248.13(A)(5), the landlord has a duty to:"Maintain the premises in such a condition as to prevent the accumulation of moisture
and the growth of mold, and to promptly respond to any notices from a tenant as provided
in subdivision A 8 of § 55-248.16;". The tenant has the duty to notify the landlord in writing of any accumulation of moisture or any visible evidence of mold in the apartment.

Here is a copy of the Virginia Residential Landlord and Tenant Act with useful information on how to resolve any problems including any actions that you can take against the landlord: http://www.dhcd.virginia.gov/HomelessnesstoHomeownership/PDFs/Landlord_Tenant_Handbook.pdf.