Tumor formation in cucurbit cultivars resulting from infection by various strains of Agrobacterium tumefaciens and Agrobacterium rhizogenes is environmentally affected. In all instances, tumors could be induced on excised cotyledons while inoculating attached cotyledons or stems resulted in no tumor formation. In addition, buttercup squash (Cucurbita maxima Duch. buttercup) was most susceptible to tumor formation, while butterbush squash (Cucurbita maxima Duch. butterbush) failed to form tumors when inoculated with any of the strains of Agrobacterium. Other tested cucurbit cultivars showed intermediate susceptibility to tumor induction by the various Agrobacterium strains.Dicotyledonous plants are susceptible to infection from two species of Gram-negative soil bacteria, Agrobacterium tumefaciens and Agrobacterium rhizogenes (2,12). The result of infection by these pathogens is a plant neoplasm, caused by the insertion of a segment of DNA, termed T-DNA, from the bacterium into the host genome (2). This T-DNA is contained on the Ti2 plasmid in A. tumefaciens and Ri plasmid in A. rhizogenes (2). These plasmids have been found to share DNA sequence homology (9), and are a requirement for bacterial virulence (16). In addition, genetically engineered forms of these plasmids have served as vehicles for gene transfer and expression in plants (7).The host range for most species ofAgrobacterium is very wide (4). Recently, however, it was reported that certain strains exhibit very high host specificity based primarily on the Ti plasmid, with a role also assigned to the chromosomal background ofthe strain (10). Further, Owens and Cress (13) Moore. In most cases, an overnight culture grown in L-media (10 g/L tryptone, 10 g/L NaCl, 5 g/L yeast extract, pH 7.5) was used as the inoculum. Occasionally, log phase cultures were used. In general, no qualitative differences were observed between these two inocula.Plants and Inoculations. Four varieties of squash (Cucurbita maxima Duch. buttercup, green hubbard, vegetable spaghetti, and butterbush) and one variety of pumpkin (Cucurbita maxima Duch. big max) were grown in a growth chamber (16 h photoperiod, 22C) in vermiculite irrigated with Hoagland solution (6). As positive controls, carrot (Daucus carota) root slices, tomato (Lycopersicum esculentum) stems, and Kalanchoe stems were used.Two protocols were attempted for tumor induction. Virulence was induced on whole plants and detached cotyledons as described by Owens and Cress (13). Stem and/or leaf wounds were made with a sterile toothpick. Approximately 10 ,ul of a bacterial suspension was spread over the wound site. Plant ages ranged form 7 to 21 d after planting. Detached cotyledons from approximately 8 d old plants were excised and surface sterilized in 10% commercial bleach for 15 min. After rinsing with sterile H20, cuts along both sides ofthe main vein were made, and inoculated with approximately 2.5 ,ul of the bacterial suspension. After incubating the cotyledons 3 d on water agar, they were transferred to Murash...

ObjectiveConcern for children exposed to elemental mercury prompted the Agency for Toxic Substances and Disease Registry and the Centers for Disease Control and Prevention to review the sources of elemental mercury exposures in children, describe the location and proportion of children affected, and make recommendations on how to prevent these exposures. In this review, we excluded mercury exposures from coal-burning facilities, dental amalgams, fish consumption, medical waste incinerators, or thimerosal-containing vaccines.Data sourcesWe reviewed federal, state, and regional programs with information on mercury releases along with published reports of children exposed to elemental mercury in the United States. We selected all mercury-related events that were documented to expose (or potentially expose) children. We then explored event characteristics (i.e., the exposure source, location).Data synthesisPrimary exposure locations were at home, at school, and at other locations such as industrial property not adequately remediated or medical facilities. Exposure to small spills from broken thermometers was the most common scenario; however, reports of such exposures are declining.Discussion and conclusionsChildhood exposures to elemental mercury often result from inappropriate handling or cleanup of spilled mercury. The information reviewed suggests that most releases do not lead to demonstrable harm if the exposure period is short and the mercury is properly cleaned up.RecommendationsPrimary prevention should include health education and policy initiatives. For larger spills, better coordination among existing surveillance systems would assist in understanding the risk factors and in developing effective prevention efforts.

Concern for children exposed to elemental mercury prompted the Agency for Toxic Substances and Disease Registry and the Centers for Disease Control and Prevention to review the sources of elemental mercury exposures in children, describe the location and proportion of children affected, and make recommendations on how to prevent these exposures. In this review, we excluded mercury exposures from coal-burning facilities, dental amalgams, fish consumption, medical waste incinerators, or thimerosal-containing vaccines. We reviewed federal, state, and regional programs with data on mercury releases along with published reports of children exposed to elemental mercury in the United States. We selected all mercury-related events that were documented to expose (or potentially expose) children. Primary exposure locations were at home, at school, and at others such as industrial property not adequately remediated or medical facilities. Exposure to small spills from broken thermometers was the most common scenario; however, reports of such exposures are declining. The information reviewed suggests that most releases do not lead to demonstrable harm if the exposure period is short and the mercury is properly cleaned up. Primary prevention should include health education and policy initiatives.

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