The topic of this dissertation is the sustainable disposal of waste materials in a way that mitigates risk to human health and the environment. A meta-analysis of organic contaminant concentrations in U.S. sewage sludge highlights the known analytes detected across 106 studies, and juxtaposes these data with a Chinese sludge analysis covering 159 studies, finding that U.S. average concentrations were higher than Chinese concentrations in 26 out of 34 tested organic chemicals. To further investigate the risk that sewage sludge poses when applied on agricultural land mixed with fertilizer as a soil amendment, a sewage sludge risk assessment that for the first time utilized Monte-Carlo simulations was performed to quantify the human health risk of metals present in sewage sludge applied on soils subject to involuntarily ingestion. This study found that while hazard indexes did not indicate a risk to humans for the metals studied, hundreds of other inorganic and organic chemicals are known to be present whose human health risks remain uncertain due to a lack of toxicological data. Among these contaminants are micro- and nanoplastics which contaminate not just sewage sludge but the entire globe. Application of existing models to the world’s oceans showed micro- and nanoplastics to constitute an important component of the total global plastic waste inventory, forecasting peak exposures of aquatic organisms (and by extension human populations) to occur in future years irrespective of what policy options will be implemented. A review of disposal options for sewage sludge illustrates the challenge of dealing with waste streams containing persistent or even indestructible contaminants such as perfluorinated organics, mass-produced fossil-fuel derived consumer plastics, and extensively mined toxic metals. The work presented here details the risks, both avoidable and unavoidable, that are present in the disposal of sewage sludge and plastics. The information presented in this dissertation may inform regulatory actions to promote environmentally responsible disposal and reuse of sewage sludge and highlights the need for industry to transition to the production of more sustainable plastics in order to reduce and ultimately eliminate sources of persistent long-term environmental pollution and their associated adverse human health and ecosystem impacts.