Produced water is generated during the operation of oil and gas wells. It contains a complex mixture of dissolved and particulate organic and inorganic substances, including naturally occurring substances (NOS) from the geological formation, such as hydrocarbons and metals, and intentionally added chemicals. This technical report provides an updated review of the composition, fate, and effects, of NOS in produced water, including field-based monitoring and surveillance related to produced water. This knowledge is essential to ensure risk-based assessment methods used in the management of produced water discharges are informed by all available evidence.