The fumigant nematicide, 1,3-dichloropropene (l,3-D VL; 'Telone' 11) and a soluble liquid formulation, 1,3-D SL were tested in a pineapple field experiment to evaluate the vapor movement of the two formulations in soil gas as well as the movement and persistence of 1,3-D SL in soil profiles. Prior to planting, 1,3-D VL (407 kg ha-') was hand-injected into the soil in two parallel rows per planting bed to approximate the practice of chisel injection. 1,3-D SL (407 kg ha-') was applied with 6 mm of water by drip irrigation through a drip tube in the center of the bed. Post-plant applications of 1,3-D SL (113 kg ha-') were made at three-month intervals during a two-crop cycle. 1,3-D concentrations in soil gas were lower at the plant line in the drip treatment compared with the 1,3-D VL treatment, owing to differences in application method and fumigant placement. 1,3-D in the vapor phase reached peak concentrations 24 h after injection in the 1,3-D VL treatment compared with a peak at 48 h in the drip treatment. Post-plant applications of 1,3-D SL resulted in a three-fold difference in peak 1,3-D soil gas concentrations between replicate applications, the concentration being inversely related to soil moisture at the time of sampling. Drip application of 1,3-D SL resulted in a relatively uniform distribution of 1,3-D across the bed and to a depth of 45 cm. There was no effect of formulation on downward movement of 1,3-D and persistence in soil profiles sampled two weeks and one month after application. Rainfall which occurred 9 days after pre-plant 1,3-D fumigation resulted in leaching of 1,3-D to a depth of 150 cm in soil profiles. Due to the short half-life of 1,3-D, significant penetration of 1,3-D in the soil was observed only when irrigation or rainfall occurred soon after application.
Analysis of pelagic clay samples from Sites 576, 578, and 581 shows that physical, acoustic, and electrical trends with increasing burial depth are related to mineralogical and diagenetic changes. The properties of interest are bulk density (p), porosity (Φ), compressional-wave velocity (1^) and velocity anisotropy (A p), and electrical resistivity (R o) and resistivity anisotropy (A r). In general, as demonstrated in particular for the brown pelagic clay, the increase in p, V p , R o , and to a lesser extent A p and A T , with increasing depth is primarily caused by decreasing Φ (and water content) as a result of compaction. The mineralogy and chemistry of the pelagic clays vary as a function of burial depth at all three sites. These variations are interpreted to reflect changes in the relative importance of detrital and diagenetic components. Mineralogical and chemical variations, however, play minor roles in determining variations in acoustic and electrical properties of the clays with increasing burial depth.
This paper is the second part of a two‐part series concerned with assessing the potential for organic chemical leaching to a ground‐water skimming tunnel in the Pearl Harbor Basin, Oahu, Hawaii, as a direct result of proposed urban development. The Pesticide Root Zone Model (PRZM) was used, after testing with field and laboratory data described in the companion paper, to make long‐term predictions of the movement of chlorpyrifos, diazinon, metribuzin, and nitrate under various recharge scenarios. The PRZM simulations revealed that, with the exception of chlorpyrifos, detectable levels of all the chemicals considered in this study may leach through the unsaturated zone to the water table from where they may eventually migrate to the skimming tunnel. The simulated concentrations in leachate reaching the water table were sufficiently low, considering subsequent mixing in the ground water, to suggest no adverse health effects. The reliability of the simulated results are laced with enough uncertainty, however, to suggest the need for monitoring for diazinon, metribuzin, and nitrate, if development does proceed. The methodology presented in this series is a first attempt at establishing a protocol for using numerical modeling, supported by field and laboratory measurements to aid in land‐use change consideration in Hawaii when nonpoint ground‐water contamination from organic chemicals is of concern.
The lagoon sediments of Enewetak Atoll in the Marshall Islands contain a large selection of fallout radionuclides as a result of 43 nuclear weapon tests conducted there between 1948 and 1958. Studies of the burial of fallout radionuclides have been conducted on the islands and in several of the large craters, but studies of their vertical distribution have been limited to about the upper 20 cm of the lagoon sediments. We have found elevated fallout radionuclide concentrations buried more deeply in the lagoon sediments and evidence of burrowing into the sediment by several species of callianassid ghost shrimp (Crustacea: Thalassinidea) which has displaced highly radioactive sediment. The burrowing activities of callianassids, which are ubiquitous on the lagoon floor, facilitate radionuclide redistribution and complicate the fallout radionuclide inventory of the lagoon.
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