UBS It noted that the world’s largest silver ETF—the iShares Silver Trust (SLV)—was one of the main drivers behind the growth in ETF trading volume; SLV’s trading volume hit a new high for the year on three of the past four days, and the Chicago Mercantile Exchange’s (CME) margin hike triggered excessive participation in SLV by retail investors.There were significant outflows on Monday, while capital flows balanced out on Tuesday.