Edible clays are consumed by diverse groups of people, especially of African descent, living in Africa and abroad, in a behavior known as geophagy. The clays are used topically as an emollient and drying agent and internally to control diarrhea. Scientific information concerning the chemical constituents and toxicity of edible clays is scarce. The aims of the present study, therefore, were to ascertain the chemical composition of white edible clays (WEC) and gray edible clays (GEC); to determine their toxicity profiles using analytical chemical methods; to test the acute and sub-acute toxicity of edible clays in their natural form as consumed; and to compare the raw and processed clays, and also to compare the latter to a proprietary drug known as ‘Mist kaolin’ (Moko®) which contains some clay along with other chemicals. Atomic absorption spectroscopy (AAS) and gas chromatography/mass spectrometry (GC/MS) were used to determine the elements present. White female Wistar mice and rats were used for the acute and sub-acute toxicity analyses, respectively. The results from AAS showed the presence of heavy metals and metalloids in both GEC and WEC, and the GC/MS revealed the presence of contaminants such as indomethacin and ethyl benzene, but quantities were below human toxicity levels. Doses of 100–500 mg/kg of either clay type could be harmful to the digestive system, but all of the tests revealed that edible clay is not toxic to humans unless very large amounts (500–1000 mg/kg of body weight) are consumed.

Acute toxicity of ammonia was investigated in four life stages of juvenile chub, Leuciscus cephalus (cyprinid fish): 1, 10, 20 and 30 days after the first feeding. The fish used for the toxicity test were reared intensively in a closed recirculation system. Each acute toxicity test duration was 96 h and lethal concentration LC1, LC50 and LC99 values were calculated for 24, 48, 72 and 96 h. The susceptibility of chub to acute ammonia toxicity decreased linearly with age and stage of development. The LC50 (48 h) values ranged from 0.62 mg L-1 of unionized ammonia nitrogen for one day after first feeding larvae to 1.73 mg L-1 for 30 days after first feeding ones. A significant linear relationship between chub larvae susceptibility to ammonia toxicity and both body weight and length was found. The critical level of unionized ammonia nitrogen for chub larvae was suggested as 0.49 mg L-1.

Fish tests must be developed for both regulatory and conservation reasons, as such testing forms an indispensable component of integrated toxicity testing strategy for the marine environment. To standardise a fish embryo test, the acute toxicity of metals and polycyclic aromatic hydrocarbons (PAHs) to early life stages (ELS) of turbot (Psetta maxima) was studied. Embryos were exposed to dilutions of cooper, cadmium, mercury, fluoranthene, phenanthrene, pyrene and naphthalene in darkness and under visible light. Hatching success, yolk sac alterations, pericardial edema, skeletal deformities and mortality were observed. The effective concentrations (EC50, EC10,) no observed effect concentration (NOEC) and the lowest observed effect concentration (LOEC) were determined at the end of the bioassays. Exposure to metals and PAHs in ecologically relevant concentrations, either in darkness or under artificial light, caused significant lethal and sublethal effects in turbot, such as alterations in yolk sac, pericardial edema and skeletal abnormalities. According to the 96 h EC50, the ranking of acute toxicity for metals was respectively: 47.4 (46.8–59.2) μg L−1 Cu; 51.5 (20.9–91.7) μg L−1 Cd, and 83.2 (62.3–125) μg L−1 Hg. For PAHs, acute toxicities were 5.2 (4.3–6) μg L−1 pyrene, 12.3 (6.4–12.7) μg L−1 fluoranthene, 52.2 (30.4–82.7) μg L−1 phenanthrene, and 142 (55–228) μg L−1 naphthalene. Pyrene was consistently the most toxic PAH. In addition, light exposures were performed and photo-enhanced toxicity was found only for fluoranthene and pyrene. Turbot embryos were found to be more tolerant to metals and PAHs than were hatched larvae. These results suggest that, considering the short duration of the ELS turbot test and its high sensitivity, it is suitable for use as a standard test for marine fish.

Steam distillates of seven Nigerian plants, Lippia adoensis Hoschst, Azadirachta indica A. Juss, Monodora tenuifolia Benth, Piper guineense Schum & Thonn, Petiveria alliacea L., Citrus sinensis L. (variety Nigerian green orange), and Cymbopogon citratus L. were tested for acute toxicity on four major insect pests. The pests were larvae of Acrae eponina Cramer, adult cotton stainer Dysdercus superstitiosus (F.), the cowpea flea beetle, Ootheca mutabilis Sahlberg and the pod sucking bug Riptortus dentipes F. Essential oils of L. adoensis, M. tenuifolia and P. guineense were toxic to the insects. O. mutabilis was the most susceptible with LD50 of 0.15, 0.32 and 0.52 respectively for M. tenuifolia, L. adoensis and P. guineense, while R. dentipes was the least susceptible. There was cessation of feeding in A. eponina treated with essential oil of C. sinensis and P. alliacea.