Synthesizing a bacterium in the lab that can break down toxic waste without negatively impacting humans or the environment is a complex and challenging process. This involves multiple fields such as biotechnology, synthetic biology, and biosafety. Here is an outline of possible steps, but please note that this requires rigorous scientific research, experimental validation, and regulatory review: 1. **Target identification and assessment**: Identify the types of toxic wastes that need to be broken down and evaluate existing biodegradation methods. Understand the chemical properties and toxicity of these wastes. 2. **Bacterial screening**: Look for bacteria that already exist in nature and have the ability to break down specific toxic substances. This can be achieved through sample collection and laboratory screening. 3. **Genetic engineering**: Use gene editing technology, such as CRISPR-Cas9, to modify selected bacteria to improve their efficiency in processing hazardous substances and reduce potential risks to the environment. Genes can be inserted or deleted to optimize their function. 4. **Metabolic pathway optimization**: Analyze and optimize the metabolic pathways of bacteria to improve their efficiency in processing toxic substances under different environmental conditions. Use synthetic biology to build efficient metabolic networks. 5. **Safety Assessment**: Conduct a comprehensive biosafety assessment to ensure that the synthesized bacteria are harmless to humans and the environment. Study their growth conditions, ecological adaptability, and possible external impacts. 6. **Laboratory Testing**: Conduct small-scale experiments in a controlled environment to observe the performance of the bacteria under different conditions and the degradation effect on the target pollutants. 7. **Risk Management and Biocontrol**: Design biocontrol measures to prevent the accidental spread of modified bacteria in the natural environment. This can include designing bacteria to survive only under specific conditions or using suicide switch mechanisms. 8. **Pilot Application**: Conduct small-scale pilots in actual application environments to verify their actual effects and safety. Closely monitor the impact and unexpected consequences. 9. **Regulatory and Ethical Review**: The synthesis and use of such bacteria must comply with relevant regulations and conduct ethical reviews to ensure compliance with social ethical standards. 10. **Public Participation and Education**: Carry out public education activities to improve society's understanding of synthetic biology and its uses and gain public support. Please note that such projects involve cutting-edge technology and complexity in biotechnology research and development, and must be carried out by professional teams in compliant experimental facilities. Before taking any step in the project, experts in the relevant field should be consulted and close cooperation with regulatory authorities should be carried out.