Lowest trophic level

Herbicides constitute a large and diverse class of pesticides that, with a few exceptions, have very low mammalian toxicity and have received relatively little attention as environmental pollutants. Much of the work in the held of ecotoxicology and much environmental risk assessment has focused on animals, especially vertebrate animals. There has perhaps been a tendency to overlook the importance of plants in the natural world. Most plants belong to the lowest trophic levels of ecosystems, and animals in higher trophic levels are absolutely dependent on them for their survival. 

Although the entry of MeHg into the base of the food web and its subsequent transfer in the lowest trophic levels are poorly understood, it is evident that the concentration of MeHg in all trophic levels is strongly correlated with its supply from methylating environments. In fish, for example, much of the modem spatial variation in mercury concentrations (within a given trophic level) can be attributed to variation in factors and processes that affect the microbial production of MeHg and its entry into oxic waters. 

No biomagnification of chromium has been observed in food chains, and concentrations are usually highest at the lowest trophic levels... 

Above- and below-ground plant parts, along with soil invertebrates, are the base (lowest trophic levels) of the terrestrial food web. Receptors at an intermediate trophic level can be exposed to pollutants that... 

Bast and von Oertzen listed energy contents of about 100 aquatic organisms with special attention to those found in the Baltic Sea [106]. Data were obtained by combustion in a modified Phillipson microcalorimeter (MBC-3) or taken from the literature and showed a range from about 12 to 29 kJ/g afdw. Highest values were observed in eggs (26.7 0.3 kJ/g afdw) and in larvae with yolk sacs (26.8 kJ/g afdw), smallest values on the lowest trophic level and in sediments [106]. 

Dibutyltin. A larger data set exists for dibutyltin, including both acute and long-term test results. The lowest concentration identified was a chronic NOEC of 0.015 mg/1 for Daphnia magna exposure to dibutyltin chloride. Long-term values were available across three trophic levels, and, therefore, an uncertainty factor of 10 was considered appropriate. 

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