We present low-frequency (80 – 240 MHz) radio observations of circular polarization in 16 isolated type III solar radio bursts using the Murchison Widefield Array (MWA) between August 2014 and November 2015. For most of the bursts, near burst onset, we find on average 9 % circular polarization at 80 MHz and 22 % at 240 MHz whereas these percentages are 5 % and 20 % near burst maximum. The polarization fractions are neither constant in time nor uniform over the spatial extents of the bursts. We measure polarization fractions as a function of burst source’s position. On average, near both burst onset and maximum, we find higher polarization near the disk center and lower polarization when the burst source is near the limb. We study total intensity (Stokes  I ), circularly polarized intensity (Stokes  V ), and polarization fraction ( | V | / I ) profiles for type III bursts with and without source motion as a function of position at times when the intensity of bursts is maximum. For the burst event with no source motion, we find symmetric profiles for Stokes  I , V , and | V | / I . We find symmetric I and V but asymmetric | V | / I profiles for burst events which have source motion. We argue that this is due to the fundamental emission at the front of a type III electron beam and motion of the burst source. We then perform spectropolarimetric imaging studies of moving burst sources and analyze their motion. At burst onset, we obtain relatively higher polarization fractions, which is considered to be due to a large contribution from fundamental plasma emission at the front of the beam. At burst maximum, the polarization fraction is lower due to the combination of fundamental and harmonic components. After peak intensity, the emission is dominated again by the fundamental component that decays until the end of a burst with lesser polarization fraction than earlier. We argue that the fundamental radiation that decays over time after peak burst intensity is strongly scattered. This pattern of fundamental, fundamental and harmonic, and then fundamental emission with time at each frequency is consistent with the interpretations of Dulk, Suzuki, and Sheridan ( Astron. Astrophys. 130 , 39, 1984 ), Robinson, Cairns, and Willes ( Astrophys. J. 422 , 870, 1994 ), and Robinson and Cairns ( Solar Phys. 181 , 363, 1998 ). We propose that scattering effects can be a viable reason for low polarization fractions in type III events. Finally, we investigate the variations of the decay time ( t d ) for three events with frequency ( f ), finding that t d ∝ f − 2.0 ± 0.1 and decreases more rapidly with increasing f compared with previous lower-frequency observations ( t d ∝ f − 1.1 ± 0.1 ). This is interpreted in terms of radial variations of the turbulence properties.