## 7 Sampling of MPs and NPs in the Aquatic Environment  
MPs and NPs are sampled through water and aquatic sediment collection plus biological specimens [154; 155; 156]. Multiple approaches for sampling MPs and NPs exist, each has its own advantages and limitations. Sampling method selection is dependent on multiple factors including the objective of the investigation, matrices to be sampled, available equipment and size limitation of target MPs [157; 158]. Overall, sampling MPs from marine environments can be categorised into three approaches as indicated in Table 7.  
Furthermore, there are multiple sampling methods that can be employed for MPs and NPs in both water and sediment. Water samples can be collected either from the water column at specific depths or the surface. It is common to use manta nets (trawls) and neuston nets when sampling surface or near-surface water [157; 159]. Their advantages include: (1) easy to use, (2) samples large volumes of water, (3) captures large number of MPs. However, certain limitations must be considered as: (1) they are expensive to acquire, (2) require a boat for use, (3) are time consuming, (4) samples are subjected to potential contamination by the tow ropes and the boat/vessel, (5) the lowest limit of MPs detection is 333 \(\upmu\)m [157; 160]. Commonly used equipment for water column sampling includes plankton nets for surface and near-surface sampling, bongo nets for deep water sampling, continuous plankton recorders (CPR), multiple opening-closing nets and near-bottom trawls [161; 162; 163]. These come with advantages and limitations, for example, plankton nets are: (1) easy and quick to use, (2) able to sample medium volumes of water, (3) have a small mesh size (\(\sim\)100 \(\upmu\)m) allowing sampling in a short period of time (i.e., under a minute) and acquires MP concentrations 30 times higher than manta nets [164]). However: (1) they are expensive, (2) require \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sampling Approach** & **Criteria** & **Application** & **Advantages** & **Limitations** \\ \hline \multirow{4}{*}{Selective Sampling} & Utilized when plastic items & & & Size limitation of detectable \\  & are large enough for & & & MPs is high and less obvious \\  & identification with the naked & & & items are easily overlooked \\  & eye, extracted directly from & & & particularly when mixed with \\  & environmental matriors. & & & other debris. \\  & Involves collecting the entire & & Collects all MPs- and NPs & Sample collection is relatively \\  & sample without decreasing its & & present within the sample & small in amount which may \\  & volume during the sampling. & & regardless of size and & negatively affect sample \\  & Used when the entire volume & & visibility. & representativeness \\  & of a bulk sample needs to be & & & Substantial loss of MPs and \\  & reduced by fast filtration & & & NPs may occur as most of the \\  & during sampling this, only & & & sample is lost/ discarded due \\  & small fraction of the sample is & & areas of samples. & to fast filtration, which is \\  & being preserved for further & & & evident in the MPs’ size being \\  & analysis. & & & smaller than the mesh size of \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The categories of sampling approaches and methods. a boat, (3) require water flow for static sampling, (4) could get clogged or break, and (5) sample lower volumes of water in comparison to manta nets [157; 165]. Other sampling tools include water intake pumps (e.g., shallow-water plankton pump (SPP), deep-water plankton pump (DPP) and submersible pump) and water collection bottles [166; 167; 168]. Water intake pumps enable sampling of large volumes of water effortlessly and provide a choice of mesh size. Nevertheless, they require equipment, and energy to work and are subjected to potential contamination by the tools, plus they could pose some difficulty when transporting them between sampling locations [154; 157].