Which type of phosphorus is bound to sediment particles, making it less bioavailable?

Particulate phosphorus is indeed the correct choice because it refers to phosphorus that is physically bound to sediment particles, making it less accessible for biological uptake by plants and microorganisms in the soil or aquatic environments. This form of phosphorus can be found in the particulate matter and is often associated with soil particles, limiting its mobility and bioavailability.

In contrast, organic phosphorus, while it can be bound in compounds, is more likely to be converted into available forms through microbial activity and decomposition. Reactive phosphorus, often considered more available to plants, can quickly convert to forms that are utilizable if the right conditions exist. Soluble phosphorus, on the other hand, is easily taken up by plants and microorganisms due to its dissolved state in water, which significantly enhances its bioavailability.

Therefore, particulate phosphorus stands out as the form that is less bioavailable due to its association with sediment, making it harder for organisms to access and utilize.