The effect of clay minerals on cadmium toxicity to bacterial production.

The effect of clays on cadmium toxicity to bacterial production and specific production was investigated in Lake Brazos, McLennan County, Texas. Bacterial production calculated from ^H-thymidine incorporation rates in samples without added cadmium ranged from 5.3x10"^ to 2.13x10"^ jj.g c 1"1 hr~l. Specific production varied between 8.1x10"® and 3.32x10"4 (Ig C ^lg C"1 hr". Cadmium significantly reduced bacterial productivity at low levels (1 mg Cd 1"--) . The response was non-linear. Reduction ranged from 79% at 1 mg Cd 1"1 to 98.4% at 20 mg 1"1. Reduction at 5 and 10 mg Cd 1"^ was 62.4% and 65.1%, respectively. Specific production dropped by 70.5% at 1 mg Cd 1"1, 82.2% at 20 mg 1"-*-, 55% at 5 mg l"-'-, and 50.4% at 10 mg Cd 1"1. Added clays increased cadmium toxicity to bacteria. Bacterial production and specific productivity were reduced by 90.7% and 85.9%, respectively, at 1 mg Cd 1"1 in samples amended with 20 mg 1"^ clay. Cadmium toxicity decreased with further additions of clay, approaching that observed in the untreated samples.