The impacts of personal care product pollution on seagrass (Zostera marina) health

The presence and proliferation of seagrass play a significant role in the condition of marine ecosystems. However, the total area of seagrass coverage has declined significantly in many places worldwide. In addition to environmental and developmental pressures, combined sewage overflows (CSOs) may be a significant additional stressor to seagrass growth and function. CSOs are a primary driver for surface water runoff and other sewage problems releasing low-quality water into the ocean. Personal care products (PCPs) are often found within wastewater and could contain harmful chemicals to the coastal environment. Here, four shampoos with different potentially harmful chemical contents were tested for their ecotoxicity to Zostera marina seedlings and juveniles at three concentrations. Shampoos A and B represented conventional commercial products containing synthetic surfactants and preservatives, while shampoos C and D were environmentally marketed formulations with milder or plant-derived ingredients. Blade lengths, photosynthesis yields, germination rates, and colour (RGB) values of the specimens were measured as health indicators. There was substantial breakage in addition to browning of blades recorded following exposure to the highest shampoo concentrations. The browning and blackened blades had significantly lower or no photosynthetic capacity while the remaining living blades maintained effective photosynthetic capacity. The germination study showed early germination in seeds exposed to higher concentration solutions and less germination overall compared to the control. These results emphasise the importance of gaining a better understanding of the potential effects that wastewater runoff and dumping events have on seagrass meadows. Building on this knowledge base will improve management and regulation enforcement strategies. Future monitoring efforts should include investigations into the concentration of shampoo residues found in both treated and unfiltered sewage.