The spoil heaps of the sulphur mines of the Negoiul Românesc volcanic cone are intensely reworked by mass movement processes which not only lead to severe sedimentation in downstream rivers, but also to the toxification of riparian Norway spruce (Picea abies (L.) Karst.) forests. Along the lateral borders of the Dumitrelul retention basin, recent sedimentation has covered P. abies trees with up to 160 cm of toxic, sulphur-rich material originating from the spoil heaps deposits. This study documents the deposition of toxic sediments and illustrates the effects that these sulphur-rich sediments have on tree growth. The results show that trees affected by sedimentation reacted with severe growth suppression and the formation of tangential rows of traumatic resin ducts, and that the intensity and persistence of growth anomalies in trees are positively correlated with local depths and granulometry of sediments.