The shells are naturally basic, too — when dissolved they have a pH of 8.3. "If pH gets below neutral 7 the shells start leeching metals and become toxic again, and that's a problem" Kohler said.

Oil major Shell (RDSa.L) has signed a five-year contract with PetroChina (601857.SS) to supply the Chinese company with carbon-neutral liquefied natural gas (LNG) cargos, Shell said on Monday.