Research▼Watch

MARCH 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 91 A

Oceanic uptake of CO2Most ocean general circulation modelsoverestimate how much anthropogenicCO2 oceans have accumulated overthe past two decades, according tonew estimates based on the globalchlorofluorocarbon (CFC) data set.The findings suggest that the oceansmay not be as large of a sink for CO2as previously thought.

Although CFC concentrations can-not be used directly to infer anthro-pogenic CO2 uptake by the oceans,they do provide information aboutthe “age” of a water mass, which isdefined as the amount of time sincethe water was in contact with the at-mosphere. Ben McNeil of PrincetonUniversity and colleagues used exist-ing data on CFCs to estimate waterages and combined that informationwith historical atmospheric CO2 levelsand equations on carbonate chemistryequilibrium to estimate dissolved in-organic carbon concentrations overthe past 20 years.

According to their results, theoceans took up a maximum of 1.9petagrams of carbon per year frommid-1980 to mid-1989 and 2.3 peta-grams of carbon per year from mid-1990 to mid-1999. Only 3 of 12international models that simulateanthropogenic CO2 uptake were closeto this upper limit. (Science 2003, 299,235–239)

Pesticides on particlesResearchers at the University ofCalifornia–Riverside have developedan analytical method to detect pesti-cide residues on single particles. Thenew approach could be used to studythe partitioning and distribution ofpesticides in the atmosphere immedi-ately following their application.

Pesticide residues find their wayinto the atmosphere through multiplepathways, including direct spray drift,volatilization from soil, and wind ero-sion of contaminated soils. Once inthe air, they can be transported over

long distances, particularly in areaswith extensive, heavy fog.

Using a real-time technique calledaerosol time-of-flight mass spectrom-etry (ATOFMS), Jeffrey R. Whiteakerand Kimberly A. Prather analyzedindividual particles that were gener-ated in the laboratory from standardsolutions of commonly used pesti-cides and from pesticide-coated soils.The MS spectra of the pesticide-containing particles had distinct massfragments that could be used asmarkers for identifying pesticides inairborne particles. In addition, theanalysis provided information on thechemicals associated with the pesti-cides in the particles, allowing the re-searchers to identify specific particletypes containing pesticides. Such in-formation could be used to determinethe source of a pesticide and how ithas been transformed in the atmos-phere. (Anal. Chem. 2003, 75, 49–56)

Sprawl threatens biodiversityUrban sprawl, not population growth,is the real threat to biodiversity, ac-cording to a study by researchers atMichigan State and StanfordUniversities. A worldwide analysis ofthe growth rate in households founddramatic increases in biodiversity“hotspots”—regions rich in speciesthat are being endangered by humanactivities—even in places with declin-ing birth rates. This trend means thatfewer people live in the average homethan in the past, and this has led tomore land and resources being usedto support the same population.

The findings support those argu-ing for “smart growth” initiatives thatlimit development in rural areas andencourage investment in cities andurban regions. However, as the au-thors point out, social factors suchas higher per capita income, lowerfertility rates, increasing divorce rates,aging populations, and fewer multi-generational family homes are drivingthis trend, and these are harder tocontrol. Moreover, critics of smart

growth claim that these laws limit thenumber of affordable homes, whichparticularly affects lower-incomefamilies.

The study, which was headed byJianguo Liu, reports that in hotspotcountries, household numbers grewon average 3.1% between 1985 and2000, and this far outstripped the av-erage 1.8% population increase. Ifhousehold numbers had remainedthe same, 155 million fewer homeswould have been needed duringthose years. Nonhotspot countries, onthe other hand, had a more modest1.7% growth in households, whichroughly matched the population in-crease. Overall, the authors expectthat household size in hotspot coun-tries will drop from an average of 4.7people in 1985 to 3.4 by 2015, whichwill require another 233 millionhomes in these increasingly crowdedareas between 2000 and 2015. (Nature2003, DOI 10.1038/nature01359)