decreasing remaining gas fraction $\mu = M_{\rm g}(t)/M_{\rm g}(0)$ as $Z(t) = y\, [-ln(\mu)]$, where $y$ as the slope is determined by the stellar yield (see e.g. textbooks like [@pag10] or reviews as e.g. by [@pra08a; @hen10]). As demonstrated by [@gar02] and [@zee01], however, the effective yields of gas-rich galaxies decrease to smaller galaxy masses. This means that their element abundances, particularly O measured in regions, are smaller than those released by a stellar population and confined in a “closed box”.

Two processes can reduce the metal abundances in the presence of old stellar populations: loss of metal-enriched gas by galactic outflows or infall of metal-poor (even pristine) intergalactic gas (IGM). It is widely believed, that a fundamental role in the chemical evolution of dIrrs is played by galactic winds, because freshly produced metals in energetic events are carried out from a shallow potential well of DGs through a wind (which will be therefore metal-enhanced). Some SBDGs are in fact characterized by galactic winds [@mar95] or by large expanding supernova type II (SNeII)-driven X-ray plumes (e.g. [@hen98; @mar02]). Studies have raised doubts to whether the expanding $\Ha$ loops, arcs, and shells mostly engulfing X-ray plumes, really imply gas expulsion from 