Global microplastic pollution at levels harmful to marine life

Poor waste management has resulted in marine plastic litter increasing worldwide, and microplastics (MP) are now detected in all marine habitats. To better understand the distribution and ecological implications of MPs, we quantify the abundance of MP in all major marine habitats through a meta-analysis of data collected by systematic review. We extracted MP densities from 334 studies covering all major water column, intertidal, inshore and offshore seabed habitats from all continents. MPs are ubiquitous, and are present in all habitats in all continents with an average (± 95%CI) global density of 37,921 ± 13,925 particles m^-2 or 0.011 kg m^-2. MP densities in sediments are at least an order of magnitude higher than in the water column. Mean MP densities are highest in Asia, in tropical regions, and in mangroves. Although sedimentary habitats such as mangroves, saltmarshes, and seagrasses are often considered potential MP sinks due to high sedimentation rates, our analysis revealed that "Blue Carbon" habitats do not consistently exhibit elevated MP densities. We found that MP densities significantly increased with decreasing minimum detectable particle size. When we rescaled MP abundance to a minimum particle size of 0.01 mm to reduce the bias, this significantly increased the estimate of mean global MP density to 57,953 ± 17,442 particles m^-2. Scaling our estimated MP densities for each habitat to a global estimate of total marine MP that exceeds 1.5 billion tonnes, far surpassing expectations based on historical plastic production. This discrepancy suggests that published MP studies may disproportionately sample polluted sites, underrepresenting broader environmental conditions. However, in the thousands of locations sampled in this meta-analysis, the mean MP densities are high enough to expect fundamental biological processes, such as growth and reproduction, of marine fauna to be significantly negatively impacted.