WE CLAIM:
1. A filter comprising at least one of a winding body containing a fibrous adsorbent
material or a laminated body containing the fibrous adsorbent material,
wherein
(a) the fibrous adsorbent material is capable of adsorbing a component dissolved in a liquid,
(b) the fibrous adsorbent material includes a base material and metal particles supported by the base material,
(c) the fibrous adsorbent material has a diameter D of 100 um or more and 600 um or less,
(d) the metal particle has a particle diameter of 1 nm or more and 1000 nm or less,
(e) the metal particles are supported by the base material in at least one form selected from the following (1) to (3):

(1) the metal particles are bonded to the base material via functional groups;
(2) the base material has holes, and the metal particles are supported in the holes; and
(3) a coating layer containing the metal particles and a polymer is provided on a surface of the base material,

(f) the winding body and the laminated body have porosity of 15% or more and 70% or less, and
(g) variation in area porosity of the winding body in a radial direction of a winding and variation in the area porosity of the laminated body in a lamination direction are 15%) or less.

2. The filter according to claim 1, wherein the base material is a monofilament or a multifilament comprising a plurality of monofilaments.
3. The filter according to claim 1 or 2, wherein the metal particles are particles containing at least one selected from the group consisting of silver, copper, iron, titanium, zirconium, and cerium.

4. The filter according to any one of claims 1 to 3, wherein the fibrous adsorbent material contains the metal particles in a proportion of 10 parts by mass or more per 100 parts by mass of the fibrous adsorbent materials.
5. The filter according to any one of claims 1 to 4,
wherein the metal particles are supported by the base material in the form of (3), and the fibrous adsorbent material includes 30 to 400 parts by mass of the coating layers per 100 parts by mass of the base materials.
6. A fluid separation method comprising:
(a) a step of separating a substance contained in a fluid from the fluid by a separation membrane, and
(b) a step of bringing the fluid into contact with the filter according to any one of claims 1 to 5,
wherein the step (b) is performed before or after the step (a).