Public school districts in the United States borrow over a trillion dollars for their facilities each year from the municipal bond market, yet more than half of these school buildings need significant repair. In this paper, we examine the relationship between a single school district infamous for its infrastructure needs, the School District of Philadelphia (SDP), and municipal bond market lending practices. Using a critical school finance framework, we ask what role municipal market lending has played in the SDP's toxic schools. After a review of relevant literatures, we estimate the total interest on debt for capital expenditure the district paid, as well as total costs of bond issuance, between 1993-2021, adjusted for inflation. We find that the district paid as much as $3.64 billion in interest on debt for capital expenditure and other purposes, and $145 million in costs of issuance for bonds during the period. Discussing the historical and policy context of this finding, we argue that Philadelphia's schools are toxic because their financing has been toxic.