Table 2.

Summary recommendations regarding exposure and design considerations in mesocosm assessment of ENM environmental hazards

Establish mesocosms only to address clearly defined questions and hypotheses, including those motivated by testing results from lower complexity microcosms, and as related to expected exposure scenarios.

Design and operate mesocosms using established authoritative principles, and aim to minimize artifacts.

Follow the recommendations for assessing hazard potentials in using individualized or microcosm experiments (Table 1)

Make experiment and exposure durations sufficiently long to best represent the exposure scenario underpinning the mesocosm design.

Anticipate and address challenges in detecting and quantifying ENMs in complex media and myriad receptors in mesocosms, such that mass balances can be performed, and bioaccumulation and trophic transfer quantified.

Attend to issues of ENMs aging, or otherwise significantly transforming, over the duration of mesocosm operation, and control for, or otherwise assess, specific outcomes related to aged materials.

Consider assessing effects and ENM interactions with co-contaminants, since they are realistic constituents of most compartments into which ENMs are released.

Anticipate, recognize, and plan to assess secondary effects on non-target receptors that contribute to ecological processes in complex systems represented by mesocosms.

Increasingly use sensitive, e.g., omics type, endpoints as they are responsive to questions and hypotheses motivating mesocosm studies.