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(abridged) Following our previous work on metal abundances of a double dampedLy-alpha system with a line-of-sight separation ~2000 km/s (Ellison & Lopez2001), we present VLT UVES abundances of 3 new systems spanning a total of\~6000 km/s at z~2.5 toward the southern QSO CTQ247. These abundances aresupplemented with echelle observations of another `double' damped Ly-alphasystem in the literature. We propose a definition in terms of velocity shift ofthe sub-class 'multiple damped Ly-alpha system', which is motivated by itspossible connection with large-scale structure. We find that the abundanceratio alpha/Fe is systematically low in multiple systems compared with singlesystems, and with a small scatter. The same behavior is found in 2 more singleDLA systems taken from the literature that show evidence of belonging to agalaxy group. After a careful investigation of possible sources of systematicerrors, we conclude that the low alpha/Fe ratios in multiple DLAs have anucleosynthetic origin. We suggest that they could be explained by reduced starformation in multiple damped Ly-alpha systems, possibly due to environmentaleffects.Comment: in press at A&

Distinct abundance patterns in multiple damped Lyαgalaxies: Evidence for truncated star formation?