to exopolysaccharide-producing bacteria located close to a biofilm. Several recent works have considered the dynamics of colloids which produce surface particles from a theoretical point of view [12–15, 21] and using simulations [13]. The key concept here is that motion of the colloid can be generated by a concentration gradient of solute, produced by the colloid itself. Most previous work has considered the case where the colloid produces solute anisotropically across its surface, resulting in directional motion. In contrast, we consider the case where solute is produced isotropically, so that the solute concentration gradient is on average symmetrical about the colloid. However, as we show here, solute production nevertheless has a strong effect on the dynamical fluctuations of the colloid. The case of an isotropic chucker has recently been considered theoretically by Golestanian [11]. Using scaling theory and linearised hydrodynamics, he predicts inertial and diffusive dynamical regimes, separated by an anomalous regime for intermediate timescales in which the mean square displacement scales as the 3/2 power of time. He further predicts that in the diffusive regime, the effective diffusion constant scales linearly with the chucking rate. In this paper, we test these predictions using numerical simulations. The question of how a solute concentration gradient influences colloid motion has some subtleties. From one point of view, both the colloid and the solute particles are large com- pared to the solvent particles; Brownian Dynamics (BD) simulations, in which the solvent is replaced by a stochastic force on the particles, are generally believed to work well in this regime [22–25]. In such a BD representation, a concentration difference of solute across the colloid surface would produce a force on the colloid f = − k$_{B}$T ∫ ˆ n cdS where c is the local concentration of solute, the integral is over the colloid surface, ˆ n is the normal to the surface, k$_{B}$ is the Boltzmann constant and T is the temperature [13]. However, such a BD representation does not take account of the details of the solvent motion close to the chucker surface. This may be important, since, as emphasised recently by Jülicher and Prost [21], hydrodynamic theory using linearised non-equilibrium thermodynamics predicts that rela- tive motion between the colloid and solvent is dependent on the existence of a surface slip velocity. In a simple view, the density of the solvent is expected rapidly to compensate any imbalances in the solute concentration field to maintain a constant overall isotropic pressure, except in a very narrow region around the colloid where molecular interactions between the colloid surface and the solute can generate a surface slip velocity. Equivalently, one might state that in order to generate a force, the configuration of solute particles relative to the 3