Terrestrial model food chain and environmental chemicals. I. Transfer of sodium [14C]pentachlorophenate between springtails and carabids.

A model soil food chain of a ruderal ecosystem has been constructed in order to study the uptake, transfer, and accumulation of [14C]pentachlorophenate (PCP-Na). The model was based on three food levels, viz. baker's yeast, collembola, and carabid beetles, and the contaminant chemical introduced was via initial food. Continuous exposure of the organisms to the test chemical resulted in a significant uptake and transfer of radiocarbon into the food chain elements. Bioaccumulation of radiocarbon in the body tissues of the organisms was low, as large amounts taken up were quickly eliminated through the excrements. The radiocarbon level of prey animals was about 100 times higher than that of their predators, but there was only small difference in concentration between collembolas and yeast. This was probably because of a faster excretion of the chemical by the beetles than by the collembolas. During the test period no conversion of [14C]PCP-Na took place in the yeast, but the collembolas and beetles metabolized 50 and 59%, respectively. Criteria are proposed for successful implementation of food chain models.

Environmental fate and distribution of sodium [14C] pentachlorophenate in a section of urban wasteland ecosystem.

An urban terrestrial microecosystem has been used under outdoor conditions to study the transfer of chemical residues within the system components. The microecosystem consisted of soil monoliths obtained from a site with an established vegetation cover dominated by goldenrod, Solidago gigantea. The microecosystem contained integrated food chain elements composed of primary producers, herbivores and carnivores. The system was stocked with indicator insect species, snails (Cepaea nemoralis) and earthworms (Allolobophora caliginosa), captured from the original site. Evaluation of the system was made using radiolabelled sodium pentachlorophenate (PCP-Na) which was applied as a single application at an equivalent rate of 5 kg ha-1. The mass balance revealed that, after 131 days, in the autumn, and after 222 days, in the winter, that 43 and 39% radiocarbon, respectively, was recoverable from the microecosystem. The unaccounted radiocarbon was very probably removed through volatilization and photomineralization of the compound. PCP residues on foliage decreased rapidly, 50% of which were metabolised within 15 days. Most of the radiocarbon remaining in the system after 131 days was in the top soil and plant litter, transmitted mainly through washing off by rain and leaf litter fall. There was a variation in the uptake of PCP-Na residues in the food chain organisms, where the total radiocarbon concentrations during the first 19 days of exposure ranged, e.g. in snails, from 3 to 0.6 micrograms g-1, in springtails from 5 to 105; in beetles (Amara fusca) from 3 to 1, in spiders from 13 to 11, and in harvestman from 31 to 77 micrograms g-1. The ecological magnification indices (EM) of all the organisms with respect to their main food source, i.e. plant litter, demonstrated no bioconcentration effects. This is attributed to the metabolism of PCP-Na by the organisms and its rapid excretion. The urban wasteland ecosystem contained in outdoor lysimeters employed as a model gives valuable information and has considerable value in predicting the ecological fate of industrial chemicals.