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In this talk, I will present a new mechanism of impurity screening in quantum critical chains, where topological defect lines of the underlying conformal field theory provide the screening channels. This leads to exotic boundary states that go beyond Cardy's types. As an example, we demonstrate impurity screening by defect in a spin-1 chain described by the SU(3)_1 WZW model, with numerical results for the spectrum and Affleck-Ludwig entropy matching the theoretical predictions.